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Nitrogen Metabolism (nitrogen + metabolism)
Selected AbstractsUNCOUPLING OF SILICON COMPARED WITH CARBON AND NITROGEN METABOLISMS AND THE ROLE OF THE CELL CYCLE IN CONTINUOUS CULTURES OF THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE) UNDER LIGHT, NITROGEN, AND PHOSPHORUS CONTROL1JOURNAL OF PHYCOLOGY, Issue 5 2002Pascal Claquin The elemental composition and the cell cycle stages of the marine diatom Thalassiosira pseudonana Hasle and Heimdal were studied in continuous cultures over a range of different light- (E), nitrogen- (N), and phosphorus- (P) limited growth rates. In all growth conditions investigated, the decrease in the growth rate was linked with a higher relative contribution of the G2+M phase. The other phases of the cell cycle, G1 and S, showed different patterns, depending on the type of limitation. All experiments showed a highly significant increase in the amount of biogenic silica per cell and per cell surface with decreasing growth rates. At low growth rates, the G2+M elongation allowed an increase of the silicification of the cells. This pattern could be explained by the major uptake of silicon during the G2+M phase and by the independence of this process on the requirements of the other elements. This was illustrated by the elemental ratios Si/C and Si/N that increased from 2- to 6-fold, depending of the type of limitation, whereas the C/N ratio decreased by 10% (E limitation) or increased by 50% (P limitation). The variations of the ratios clearly demonstrate the uncoupling of the Si metabolism compared with the C and N metabolisms. This uncoupling enabled us to explain that in any of the growth condition investigated, the silicification of the cells increased at low growth rates, whereas carbon and nitrogen cellular content are differently regulated, depending of the growth conditions. [source] AKIN,1 is Involved in the Regulation of Nitrogen Metabolism and Sugar Signaling in ArabidopsisJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 5 2009Xiao-Fang Li Abstract Sucrose non-fermenting-1-related protein kinase 1 (SnRK1) has been located at the heart of the control of metabolism and development in plants. The active SnRK1 form is usually a heterotrimeric complex. Subcellular localization and specific target of the SnRK1 kinase are regulated by specific beta subunits. In Arabidopsis, there are at least seven genes encoding beta subunits, of which the regulatory functions are not yet clear. Here, we tried to study the function of one beta subunit, AKIN,1. It showed that AKIN,1 expression was dramatically induced by ammonia nitrate but not potassium nitrate, and the investigation of AKIN,1 transgenic Arabidopsis and T-DNA insertion lines showed that AKIN,1 negatively regulated the activity of nitrate ruductase and was positively involved in sugar repression in early seedling development. Meanwhile AKIN,1 expression was reduced upon sugar treatment (including mannitol) and did not affect the activity of sucrose phosphate synthase. The results indicate that AKIN,1 is involved in the regulation of nitrogen metabolism and sugar signaling. [source] Seasonal variations in nitrate reductase activity and internal N pools in intertidal brown algae are correlated with ambient nitrate concentrationsPLANT CELL & ENVIRONMENT, Issue 6 2007ERICA B. YOUNG ABSTRACT Nitrogen metabolism was examined in the intertidal seaweeds Fucus vesiculosus, Fucus serratus, Fucus spiralis and Laminaria digitata in a temperate Irish sea lough. Internal NO3 - storage, total N content and nitrate reductase activity (NRA) were most affected by ambient NO3 - , with highest values in winter, when ambient NO3 - was maximum, and declined with NO3 - during summer. In all species, NRA was six times higher in winter than in summer, and was markedly higher in Fucus species (e.g. 256 ± 33 nmol NO3 - min,1 g,1 in F. vesiculosus versus 55 ± 17 nmol NO3 - min,1 g,1 in L. digitata). Temperature and light were less important factors for N metabolism, but influenced in situ photosynthesis and respiration rates. NO3 - assimilating capacity (calculated from NRA) exceeded N demand (calculated from net photosynthesis rates and C : N ratios) by a factor of 0.7,50.0, yet seaweeds stored significant NO3 - (up to 40,86 µmol g,1). C : N ratio also increased with height in the intertidal zone (lowest in L. digitata and highest in F. spiralis), indicating that tidal emersion also significantly constrained N metabolism. These results suggest that, in contrast to the tight relationship between N and C metabolism in many microalgae, N and C metabolism could be uncoupled in marine macroalgae, which might be an important adaptation to the intertidal environment. [source] A comparative proteomic evaluation of culture grown vs nodule isolated Bradyrhizobium japonicumPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 10 2006Annamraju D. Sarma Abstract Total protein extract of Bradyrhizobium japonicum cultivated in HM media were resolved by 2-D PAGE using narrow range IPG strips. More than 1200,proteins were detected, of which nearly 500,proteins were analysed by MALDI-TOF and 310,spots were tentatively identified. The present study describes at the proteome level a significant number of metabolic pathways related to important cellular events in free-living B.,japonicum. A comparative analysis of proteomes of free-living and nodule residing bacteria revealed major differences and similarities between the two states. Proteins related to fatty acid, nucleic acid and cell surface synthesis were significantly higher in cultured cells. Nitrogen metabolism was more pronounced in bacteroids whereas carbon metabolism was similar in both states. Relative percentage of proteins related to global functions like protein synthesis, maturation & degradation and membrane transporters were similar in both forms, however, different proteins provided these functions in the two states. [source] Purification of three aminotransferases from Hydrogenobacter thermophilus TK-6 , novel types of alanine or glycine aminotransferaseFEBS JOURNAL, Issue 8 2010Enzymes, catalysis Aminotransferases catalyse synthetic and degradative reactions of amino acids, and serve as a key linkage between central carbon and nitrogen metabolism in most organisms. In this study, three aminotransferases (AT1, AT2 and AT3) were purified and characterized from Hydrogenobacter thermophilus, a hydrogen-oxidizing chemolithoautotrophic bacterium, which has been reported to possess unique features in its carbon and nitrogen anabolism. AT1, AT2 and AT3 exhibited glutamate:oxaloacetate aminotransferase, glutamate:pyruvate aminotransferase and alanine:glyoxylate aminotransferase activities, respectively. In addition, both AT1 and AT2 catalysed a glutamate:glyoxylate aminotransferase reaction. Interestingly, phylogenetic analysis showed that AT2 belongs to aminotransferase family IV, whereas known glutamate:pyruvate aminotransferases and glutamate:glyoxylate aminotransferases are members of family I,. In contrast, AT3 was classified into family I, distant from eukaryotic alanine:glyoxylate aminotransferases which belong to family IV. Although Thermococcus litoralis alanine:glyoxylate aminotransferase is the sole known example of family I alanine:glyoxylate aminotransferases, it is indicated that this alanine:glyoxylate aminotransferase and AT3 are derived from distinct lineages within family I, because neither high sequence similarity nor putative substrate-binding residues are shared by these two enzymes. To our knowledge, this study is the first report of the primary structure of bacterial glutamate:glyoxylate aminotransferase and alanine:glyoxylate aminotransferase, and demonstrates the presence of novel types of aminotransferase phylogenetically distinct from known eukaryotic and archaeal isozymes. [source] Detection of a homotetrameric structure and protein,protein interactions of Paracoccidioides brasiliensis formamidase lead to new functional insightsFEMS YEAST RESEARCH, Issue 1 2010Clayton Luiz Borges Abstract Paracoccidioides brasiliensis causes paracoccidioidomycosis, a systemic mycosis in Latin America. Formamidases hydrolyze formamide, putatively plays a role in fungal nitrogen metabolism. An abundant 45-kDa protein was identified as the P. brasiliensis formamidase. In this study, recombinant formamidase was overexpressed in bacteria and a polyclonal antibody to this protein was produced. We identified a 180-kDa protein species reactive to the antibody produced in mice against the P. brasiliensis recombinant purified formamidase of 45 kDa. The 180-kDa purified protein yielded a heat-denatured species of 45 kDa. Both protein species of 180 and 45 kDa were identified as formamidase by peptide mass fingerprinting using MS. The identical mass spectra generated by the 180 and the 45-kDa protein species indicated that the fungal formamidase is most likely homotetrameric in its native conformation. Furthermore, the purified formamidase migrated as a protein of 191 kDa in native polyacrylamide gel electrophoresis, thus revealing that the enzyme forms a homotetrameric structure in its native state. This enzyme is present in the fungus cytoplasm and the cell wall. Use of a yeast two-hybrid system revealed cell wall membrane proteins, in addition to cytosolic proteins interacting with formamidase. These data provide new insights into formamidase structure as well as potential roles for formamidase and its interaction partners in nitrogen metabolism. [source] Regulation of nitrogen metabolism in Mycobacterium tuberculosis: A comparison with mechanisms in Corynebacterium glutamicum and Streptomyces coelicolorIUBMB LIFE, Issue 10 2008Catriona Harper Abstract The mechanisms governing the regulation of nitrogen metabolism in Corynebacterium glutamicum and Streptomyces coelicolor have been extensively studied. These Actinomycetales are closely related to the Mycobacterium genus and may therefore serve as a models to elucidate the cascade of nitrogen signalling in other mycobacteria. Some factors involved in nitrogen metabolism in Mycobacterium tuberculosis have been described, including glutamine synthetase and its adenylyltransferase, but not much data concerning the other components involved in the signalling cascade is available. In this review a comparative study of factors involved in nitrogen metabolism in C. glutamicum and S. coelicolor is made to identify similarities with M. tuberculosis on both a genomic and proteomic level. This may provide insight into a potential global mechanism of nitrogen control in Mycobacterium tuberculosis. © 2008 IUBMB IUBMB Life, 60(10): 643,650, 2008 [source] Metabolic and productive response to ruminal protein degradability in early lactation cows fed untreated or xylose-treated soybean meal-based dietsJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 6 2009M. Jahani-Moghadam Summary Effects of different dietary rumen undegradable (RUP) to degradable (RDP) protein ratios on ruminal nutrient degradation, feed intake, blood metabolites and milk production were determined in early lactation cows. Four multiparous (43 ± 5 days in milk) and four primiparous (40 ± 6 days in milk) tie-stall-housed Holstein cows were used in a duplicated 4 × 4 Latin square design with four 21-day periods. Each period had 14-day of adaptation and 7-day of sampling. Diets contained on a dry matter (DM) basis, 23.3% alfalfa hay, 20% corn silage and 56.7% concentrate. Cows were first offered alfalfa hay at 7:00, 15:00 and 23:00 hours, and 30 min after each alfalfa hay delivery were offered a mixture of corn silage and concentrate. Treatments were diets with RUP:RDP ratios of (i) 5.2:11.6 (control), (ii) 6.1:10.6, (iii) 7.1:9.5 and (iv) 8.1:8.5, on a dietary DM% basis. Different RUP:RDP ratios were obtained by partial and total replacement of untreated soybean meal (SBM) with xylose-treated SBM (XSBM). In situ study using three rumen-cannulated non-lactating cows showed that DM and crude protein (CP) of SBM had greater rapidly degradable fractions. The potentially degradable fractions were degraded more slowly in XSBM. Treatment cows produced greater milk, protein, lactose, solids-non-fat and total solids than control cows. Increasing RUP:RDP reduced blood urea linearly. Feed costs dropped at RUP:RDP ratios of 6.1:10.6 and 7.1:9.5, but not at 8.1:8.5, compared with the 5.2:11.6 ratio. Intake of DM and CP, rumen pH, blood glucose, albumin and total protein, faecal and urine pH, changes in body weight and body condition score, and milk lactose and solids-non-fat percentages did not differ among treatments. Results provide evidence that increasing dietary RUP:RDP ratio from 5.2:11.6 to 7.1:9.5 optimizes nitrogen metabolism and milk production and reduces feed costs in early lactation cows. Reduced blood urea suggests reprodutive benefits. [source] Macronutrient digestibility, nitrogen balance, plasma indicators of protein metabolism and mineral absorption in horses fed a ration rich in sugar beet pulpJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 9-10 2004A. F. S. Olsman Summary In a cross-over study with six mature horses, the effect of iso-energetic replacement of dietary glucose by beet pulp on macronutrient digestibility, nitrogen metabolism and mineral absorption was studied. The test ration contained 25% beet pulp in the total dietary dry matter. Beet pulp feeding significantly lowered crude fat and non-structural carbohydrate digestibility, but had no significant effect on digestibility of other macronutrients, faecal and urinary nitrogen excretion and the faecal to urinary nitrogen excretion quotient. However, on the beet pulp diet, plasma ammonia and creatinin concentrations were significantly lower than on the glucose diet. No diet effect on magnesium absorption was observed. It is suggested that dietary beet pulp stimulates the conversion of ammonia into urea. [source] The role of GAP1 gene in the nitrogen metabolism of Saccharomyces cerevisiae during wine fermentationJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2009R. Chiva Abstract Aim:, The aim of this study was to analyse the relevance of the general amino acid permease gene (GAP1) of the wine yeast Saccharomyces cerevisiae on nitrogen metabolism and fermentation performance. Methods and Results:, We constructed a gap1 mutant in a wine strain. We compared fermentation rate, biomass production and nitrogen consumption between the gap1 mutant and its parental strain during fermentations with different nitrogen concentrations. The fermentation capacity of the gap1 mutant strain was impaired in the nitrogen-limited and -excessive conditions. The nitrogen consumption rate between the wild strain and the mutant was different for some amino acids, especially those affected by nitrogen catabolite repression (NCR). The deletion of GAP1 gene also modified the gene expression of other permeases. Conclusions:, The Gap1 permease seems to be important during wine fermentations with low and high nitrogen content, not only because of its amino acid transporter role but also because of its function as an amino acid sensor. Significance and Impact of the Study:, A possible biotechnological advantage of a gap1 mutant is its scarce consumption of arginine, whose metabolism has been related to the production of the carcinogenic ethyl carbamate. [source] AKIN,1 is Involved in the Regulation of Nitrogen Metabolism and Sugar Signaling in ArabidopsisJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 5 2009Xiao-Fang Li Abstract Sucrose non-fermenting-1-related protein kinase 1 (SnRK1) has been located at the heart of the control of metabolism and development in plants. The active SnRK1 form is usually a heterotrimeric complex. Subcellular localization and specific target of the SnRK1 kinase are regulated by specific beta subunits. In Arabidopsis, there are at least seven genes encoding beta subunits, of which the regulatory functions are not yet clear. Here, we tried to study the function of one beta subunit, AKIN,1. It showed that AKIN,1 expression was dramatically induced by ammonia nitrate but not potassium nitrate, and the investigation of AKIN,1 transgenic Arabidopsis and T-DNA insertion lines showed that AKIN,1 negatively regulated the activity of nitrate ruductase and was positively involved in sugar repression in early seedling development. Meanwhile AKIN,1 expression was reduced upon sugar treatment (including mannitol) and did not affect the activity of sucrose phosphate synthase. The results indicate that AKIN,1 is involved in the regulation of nitrogen metabolism and sugar signaling. [source] PRIMARY CARBON AND NITROGEN METABOLIC GENE EXPRESSION IN THE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE): DIEL PERIODICITY AND EFFECTS OF INORGANIC CARBON AND NITROGEN,JOURNAL OF PHYCOLOGY, Issue 5 2009Espen Granum Diel periodicity and effects of inorganic carbon (Ci) and NO3, on the expression of 11 key genes for primary carbon and nitrogen metabolism, including potential C4 photosynthesis, in the marine diatom Thalassiosira pseudonana Hasle et Heimdal were investigated. Target gene transcripts were measured by quantitative reverse transcriptase,PCR, and some of the gene-encoded proteins were analyzed by Western blotting. The diatom was grown with a 12 h photoperiod at two different Ci concentrations maintained by air-equilibration with either 380 ,L · L,1 (near-ambient) or 100 ,L · L,1 (low) CO2. Transcripts of the principal Ci and NO3, assimilatory genes RUBISCO LSU (rbcL) and nitrate reductase displayed very strong diel oscillations with peaks at the end of the scotophase. Considerable diel periodicities were also exhibited by the ,-carboxylase genes phosphoenolpyruvate carboxylase (PEPC1 and PEPC2) and phosphoenolpyruvate carboxykinase (PEPCK), and the Benson,Calvin cycle gene sedoheptulose,bisphosphatase (SBPase), with peaks during mid- to late scotophase. In accordance with the transcripts, there were substantial diel periodicities in PEPC1, PEPC2, PEPCK, and especially rbcL proteins, although they peaked during early to mid-photophase. Inorganic carbon had some transient effects on the ,-carboxylase transcripts, and glycine decarboxylase P subunit was highly up-regulated by low Ci concentration, indicating increased capacity for photorespiration. Nitrogen-starved cells had reduced amounts of carbon metabolic gene transcripts, but the PEPC1, PEPC2, PEPCK, and rbcL transcripts increased rapidly when NO3, was replenished. The results suggest that the ,-carboxylases in T. pseudonana play key anaplerotic roles but show no clear support for C4 photosynthesis. [source] ROLE OF GLUTAMATE DEHYDROGENASE AND GLUTAMINE SYNTHETASE IN CHLORELLA VULGARIS DURING ASSIMILATION OF AMMONIUM WHEN JOINTLY IMMOBILIZED WITH THE MICROALGAE-GROWTH-PROMOTING BACTERIUM AZOSPIRILLUM BRASILENSE,JOURNAL OF PHYCOLOGY, Issue 5 2008Luz E. De-Bashan Enzymatic activities of glutamate dehydrogenase (GDH) and glutamine synthetase (GS) participating in the nitrogen metabolism and related ammonium absorption were assayed after the microalga Chlorella vulgaris Beij. was jointly immobilized with the microalgae-growth-promoting bacterium Azospirillum brasilense. At initial concentrations of 3, 6, and 10 mg · L,1 NH4+, joint immobilization enhances growth of C. vulgaris but does not affect ammonium absorption capacity of the microalga. However, at 8 mg · L,1 NH4+, joint immobilization enhanced ammonium absorption by the microalga without affecting the growth of the microalgal population. Correlations between absorption of ammonium per cell and per culture showed direct (negative and positive) linear correlations between these parameters and microalga populations at 3, 6, and 10 mg · L,1 NH4+, but not at 8 mg · L,1 NH4+, where the highest absorption of ammonium occurred. In all cultures, immobilized and jointly immobilized, having the four initial ammonium concentrations, enzymatic activities of Chlorella are affected by A. brasilense. Regardless of the initial concentration of ammonium, GS activity in C. vulgaris was always higher when jointly immobilized and determined on a per-cell basis. When jointly immobilized, only at an initial concentration of 8 mg · L,1 NH4+ was GDH activity per cell higher. [source] IDENTIFICATION AND COMPARATIVE GENOMIC ANALYSIS OF SIGNALING AND REGULATORY COMPONENTS IN THE DIATOM THALASSIOSIRA PSEUDONANA,JOURNAL OF PHYCOLOGY, Issue 3 2007Anton Montsant Diatoms are unicellular brown algae that likely arose from the endocytobiosis of a red alga into a single-celled heterotroph and that constitute an algal class of major importance in phytoplankton communities around the globe. The first whole-genome sequence from a diatom species, Thalassiosira pseudonana Hasle et Heimdal, was recently reported, and features that are central to diatom physiology and ecology, such as silicon and nitrogen metabolism, iron uptake, and carbon concentration mechanisms, were described. Following this initial study, the basic cellular systems controlling cell signaling, gene expression, cytoskeletal structures, and response to stress have been cataloged in an attempt to obtain a global view of the molecular foundations that sustain such an ecologically successful group of organisms. Comparative analysis with several microbial, plant, and metazoan complete genome sequences allowed the identification of putative membrane receptors, signaling proteins, and other components of central interest to diatom ecophysiology and evolution. Thalassiosira pseudonana likely perceives light through a novel phytochrome and several cryptochrome photoreceptors; it may lack the conserved RHO small-GTPase subfamily of cell-polarity regulators, despite undergoing polarized cell-wall synthesis; and it possesses an unusually large number of heat-shock transcription factors, which may indicate the central importance of transcriptional responses to environmental stress. The availability of the complete gene repertoire will permit a detailed biochemical and genetic analysis of how diatoms prosper in aquatic environments and will contribute to the understanding of eukaryotic evolution. [source] Biostimulant activity of two protein hydrolyzates in the growth and nitrogen metabolism of maize seedlingsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2009Andrea Ertani Abstract Two protein hydrolyzate,based fertilizers (PHFs), one from alfalfa (AH) and one from meat flour (MFH), were studied chemically and biologically. AH and MFH revealed a different degree of hydrolysis and a different amino acid composition. The biostimulant activity was investigated using two specific and sensitive bioassays of auxins and gibberellins. Extracts of AH and MFH elicited a gibberellin-like activity and a weak auxin-like one. To improve our understanding of the biostimulant activity, AH and MFH were supplied to maize plants and their effect on growth and nitrate metabolism was studied. Both PHFs increased root and leaf growth and induced morphological changes in root architecture. Besides, the treatments increased nitrate reductase (NR) and glutamine synthetase (GS) activities, suggesting a positive role of the two hydrolyzates in the induction of nitrate conversion into organic nitrogen. Moreover, treatments enhanced GS1 and GS2 isoforms in maize leaves. The latter isoform, amounting to 5- to 7-fold the level of the former, appears to be a superior form in the assimilation of ammonia. The high NR and GS activities together with the high induction of GS isoforms indicate a stimulatory effect of the two PHFs on the assimilation of nitrate. In addition, a role of amino acids and small peptides of the two PHFs is suggested in the regulation of the hormone-like activity and nitrogen pathway. [source] Effect of apoE/ATP-containing liposomes on hepatic energy stateLIVER INTERNATIONAL, Issue 5 2003S. Chaïb Abstract: Background/Aims: ATP-containing liposomes partially prevent ATP depletion in the cold-stored liver. As hepatocytes can specifically bind apoE, we investigated whether the addition of apoE to large (200 nm) ATP-containing liposomes increases their uptake by the liver and further improves hepatic energy stores. Methods: Livers from fasted male Hartley guinea-pigs (231±3 g) were perfused for 90 min under our standard conditions (Control, n=6) or after a single bolus addition of plain liposomes (Lip, n=6), ATP (5 ,mol)-containing liposomes (ATP-Lip, n=6) or apoE/ATP-containing liposomes (0.8 or 8 mg apoE/g phospholipids; apoE1-Lip and apoE10-Lip, respectively, n=6 in each group). Liposome uptake and its impact on energy and nitrogen metabolism were studied. Results: At its highest concentration, apoE significantly increased liposome uptake (apoE10-Lip:,9.17±0.69 vs apoE1-Lip:,6.18±0.44 vs ATP-Lip:,6.40±0.88 nmol min,1 g,1; P<0.05). This was associated with a significant increase in intrahepatic ATP (apoE10-Lip: 1033±137 vs apoE1-Lip: 811±98 and ATP-Lip: 648±36 nmol g,1; P<0.05), which was restored to its level in non-perfused livers. Hepatic viability and nitrogen metabolism were not affected. Conclusions: Hepatic ATP content being a key factor in the maintenance of liver graft function, apoE/ATP-containing liposomes should be useful in liver preservation for transplantation. [source] Of blood, brains and bacteria, the Amt/Rh transporter family: emerging role of Amt as a unique microbial sensorMOLECULAR MICROBIOLOGY, Issue 1 2009Pier-Luc Tremblay Summary Members of the Amt/Rh family of transporters are found almost ubiquitously in all forms of life. However, the molecular state of the substrate (NH3 or NH4+) has been the subject of active debate. At least for bacterial Amt proteins, the model emerging from computational, X-ray crystal and mutational analysis is that NH4+ is deprotonated at the exterior, conducted through the membrane as NH3, and reprotonated at the cytoplasmic interface. A proton concomitantly is transferred from the exterior to the interior, although the mechanism is unclear. Here we discuss recent evidence indicating that an important function of at least some eukaryotic and bacterial Amts is to act as ammonium sensors and regulate cellular metabolism in response to changes in external ammonium concentrations. This is now well documented in the regulation of yeast pseudohyphal development and filamentous growth. As well, membrane sequestration of GlnK, a PII signal transduction protein, by AmtB has been shown to regulate nitrogenase in some diazotrophs, and nitrogen metabolism in some Gram-positive bacteria. Formation of GlnK,AmtB membrane complexes might have other, as yet undiscovered, regulatory roles. This possibility is emphasized by the discovery in some genomes of genes for chimeric Amts with fusions to various regulatory elements. [source] Control of nitrogen metabolism by Bacillus subtilis glutamine synthetaseMOLECULAR MICROBIOLOGY, Issue 2 2008Abraham L. Sonenshein Summary Two recent papers describe the molecular mechanism by which the activity of GlnR, the repressor of the glutamine synthetase operon in Bacillus subtilis, is stimulated by glutamine-bound (i.e. feedback-inhibited) glutamine synthetase (FBI-GS). Remarkably, FBI-GS acts as a molecular chaperone to stabilize the association of GlnR dimers with their DNA binding sites. This mechanism allows the cell to shut off synthesis of GS, and hence of glutamine, when both the enzyme and its product are in excess. FBI-GS also regulates the activity of TnrA, the global regulator of nitrogen metabolism genes, but by a very different mechanism. Thus, the same enzyme,metabolite complex has two different roles in transcriptional regulation. [source] The role of low soil temperature in the inhibition of growth and PSII function during dark chilling in soybean genotypes of contrasting tolerancePHYSIOLOGIA PLANTARUM, Issue 1 2007Abram J. Strauss Dark chilling affects growth and yield of warm-climate crops such as soybean [Glycine max (L.) Merr.]. Several studies have investigated chilling-stress effects on photosynthesis and other aspects of metabolism, but none have compared effects of whole-plant chilling (WPC; shoots and roots) with that of aboveground chilling in legumes. This is important because low root temperatures might induce additional constraints, such as inhibition of N2 fixation, thereby aggravating chilling-stress symptoms. Effects of dark chilling on PSII, shoot growth, leaf ureide content and photosynthetic capacity were studied in two soybean genotypes, Highveld Top (chilling tolerant) and PAN809 (chilling sensitive), in experiments comparing effects of WPC with that of shoot chilling (SC). Both treatments inhibited shoot growth in PAN809 but not Highveld Top. Also, WPC in PAN809 caused a decrease in leaf ureide content followed by severe chlorosis and alterations in O-J-I-P fluorescence-rise kinetics, distinct from SC. A noteworthy difference was the appearance of a ,K peak in the O-J-I-P fluorescence rise in response to WPC. These genotypic and treatment differences also reflected in the degree of inhibition of CO2 assimilation rates. The appearance of a ,K peak, coupled with growth inhibition, reduced ureide content, chlorosis and lower CO2 assimilation rates, provides mechanistic information about how WPC might have aggravated chilling-stress symptoms in PAN809. We introduce a model explaining how chilling soil temperatures might trigger N-limitation in sensitive genotypes and how characteristic changes in O-J-I-P fluorescence-rise kinetics are linked to changes in carbon and nitrogen metabolism. [source] Nitrate uptake and reduction in higher and lower plantsPLANT CELL & ENVIRONMENT, Issue 10 2000R. Tischner ABSTRACT The nitrogen compounds nitrate and ammonium are the minerals that plants need in large quantities and which limit their growth in temperate zones. The nitrate assimilation pathway starts with nitrate uptake followed by nitrate reduction resulting in ammonium which is fixed into the amino acids glutamine and glutamate in most plants. This review concentrates on nitrate uptake and nitrate reduction with respect to higher and lower plants. The physiology and the progress in molecular approaches of both processes are considered. For nitrate uptake the well-established uptake systems are discussed and special attention is drawn to nitrate sensing and the nitrate carrier. Knowledge, particularly on nitrate sensing is rare, but it seems to be the first step in a signal transduction chain triggered by nitrate. Therefore further work should consider this topic more frequently. For nitrate reductase the focus is on the post-translational modification as a regulatory tool for nitrate assimilation, on the intersections of carbon and nitrogen metabolism and on the molecular approaches. A few remarks on how environmental conditions affect nitrate assimilation are also included. Further progress is needed to understand the transduction of positive and negative signals from the environment affecting the expression of genes coding for the nitrate assimilating pathway. [source] The prion domain of yeast Ure2P induces autocatalytic formation of amyloid fibers by a recombinant fusion proteinPROTEIN SCIENCE, Issue 3 2000Martin Schlumpberger Abstract The Ure2 protein from Saccharomyces cerevisiae has been proposed to undergo a prion-like autocatalytic conformational change, which leads to inactivation of the protein, thereby generating the [URE3] phenotype. The first 65 amino acids, which are dispensable for the cellular function of Ure2p in nitrogen metabolism, are necessary and sufficient for [URE3] (Masison & Wickner, 1995), leading to designation of this domain as the Ure2 prion domain (UPD). We expressed both UPD and Ure2 as glutathione- S -transferase (GST) fusion proteins in Escherichia coli and observed both to be initially soluble. Upon cleavage of GST-UPD by thrombin, the released UPD formed ordered fibrils that displayed amyloid-like characteristics, such as Congo red dye binding and green-gold birefringence. The fibrils exhibited high ,-sheet content by Fourier transform infrared spectroscopy. Fiber formation proceeded in an autocatalytic manner. In contrast, the released, full-length Ure2p formed mostly amorphous aggregates; a small amount polymerized into fibrils of uniform size and morphology. Aggregation of Ure2p could be seeded by UPD fibrils. Our results provide biochemical support for the proposal that the [URE3] state is caused by a self-propagating inactive form of Ure2p. We also found that the uncleaved GST-UPD fusion protein could polymerize into amyloid fibrils by a strictly autocatalytic mechanism, forcing the GST moiety of the protein to adopt a new, ,-sheet-rich conformation. The findings on the GST-UPD fusion protein indicate that the ability of the prion domain to mediate a prion-like conversion process is not specific for or limited to the Ure2p. [source] Regulation of secondary metabolism by the carbon,nitrogen status in tobacco: nitrate inhibits large sectors of phenylpropanoid metabolismTHE PLANT JOURNAL, Issue 4 2006Christina Fritz Summary Interactions between nitrogen and carbon metabolism modulate many aspects of the metabolism, physiology and development of plants. This paper investigates the contribution of nitrate and nitrogen metabolism to the regulation of phenylpropanoid and nicotine synthesis. Wild-type tobacco was grown on 12 or 0.2 mm nitrate and compared with a nitrate reductase-deficient mutant [Nia30(145)] growing on 12 mm nitrate. Nitrate-deficient wild-type plants accumulate high levels of a range of phenylpropanoids including chlorogenic acid, contain high levels of rutin, are highly lignified, but contain less nicotine than nitrogen-replete wild-type tobacco. Nia30(145) resembles nitrate-deficient wild-type plants with respect to the levels of amino acids, but accumulates large amounts of nitrate. The levels of phenylpropanoids, rutin and lignin resemble those in nitrogen-replete wild-type plants, whereas the level of nicotine resembles that in nitrate-deficient wild-type plants. Expression arrays and real time RT-PCR revealed that a set of genes required for phenylpropanoid metabolism including PAL, 4CL and HQT are induced in nitrogen-deficient wild-type plants but not in Nia30(145). It is concluded that nitrogen deficiency leads to a marked shift from the nitrogen-containing alkaloid nicotine to carbon-rich phenylpropanoids. The stimulation of phenylpropanoid metabolism is triggered by changes of nitrate, rather than downstream nitrogen metabolites, and is mediated by induction of a set of enzymes in the early steps of the phenylpropanoid biosynthetic pathway. [source] Influence of dietary l -carnitine on growth, biological traits and meat quality in TilapiaAQUACULTURE RESEARCH, Issue 12 2009Shuenn-Der Yang Abstract This study was designed to determine whether l -carnitine supplementation is necessary in a tilapia diet containing low-fish meal and a high lipid level, which is beneficial economically and for the environment. The effects of dietary l -carnitine on the growth, body composition, blood traits and post-thaw drip from muscle in hybrid tilapia were investigated. Five isonitrogenous and isocaloric diets were fed to the fish with a mean body weight of 141.7 g for 168 days. The control diet contained fish meal as the major protein source with 7% lipid. Other diets contained 7% or 12% lipid, in which fish meal was largely replaced by plant proteins, and supplemented with l -carnitine or not. Results showed that supplemental dietary l -carnitine did not affect the growth performance, feed efficiency or protein efficiency ratio, while the supplementation significantly reduced the mesenteric fat ratio. Whole body and muscle proximate compositions were unaltered by any dietary treatment. The total plasma lipid, triacylglycerol and cholesterol values of tilapia fed diets with alternative plant proteins were significantly lower than those of the control fish, whereas increasing the dietary lipid content increased the aforementioned blood traits. A decrease in plasma ammonia and an increase in urea were observed in dietary l -carnitine-supplemented fish. Post-thaw drip from muscle was reduced in fish fed supplemental dietary l -carnitine. The observations of this study revealed that neither the growth performance nor the feed utilization of hybrid tilapia was improved by a dietary l -carnitine treatment, but that it did lead to a reduced mesenteric fat ratio, altered nitrogen metabolism and improved meat quality. [source] Effect of dietary protein level on growth, survival and ammonia efflux rate of Litopenaeus vannamei (Boone) raised in a zero water exchange culture systemAQUACULTURE RESEARCH, Issue 9 2005Silvia Gómez-Jiménez Abstract Litopenaeus vannamei postlarvae (1.96±0.07 g) were reared in a zero water exchange system for 25 days at 28°C. They were fed four commercial diets containing 25%, 30%, 35% or 40% crude protein in three replicate aquaria per dietary treatment. Total ammonia, nitrite, nitrate and pH were monitored weekly and total ammonia levels were additionally measured every 3 days using the flow injection analysis method. Total ammonia efflux rates were measured at days 0, 14 and 21, and survival and growth rates were recorded at the end of the experiment. No significant differences between water quality parameters such as temperature, salinity, dissolved oxygen and pH were found. Nitrite concentration remained low in all dietary treatments up to the second week increasing considerably from day 14 onwards suggesting the initiation of the nitrification process. Water total ammonia of all experimental groups exhibited a gradual increase up to day 13; however, following this time ammonia levels of all experimental groups decreased, probably due to either the action of bacterial nitrification or ammonia-N uptake by the animals. High ammonia efflux rates were recorded at day 14, especially after the first hour of immersion in the 25% protein group, but no significant changes occurred in any experimental group after 3 h. No significant differences in weight gain, final weight or survival of shrimp were observed under these experimental conditions. The importance of zero water exchange systems and their effects on the nitrogen metabolism of crustaceans are discussed. [source] Bioengineering nitrogen acquisition in rice: can novel initiatives in rice genomics and physiology contribute to global food security?BIOESSAYS, Issue 6 2004Dev T. Britto Rice is the most important crop species on earth, providing staple food for 70% of the world's human population. Over the past four decades, successes in classical breeding, fertilization, pest control, irrigation and expansion of arable land have massively increased global rice production, enabling crop scientists and farmers to stave off anticipated famines. If current projections for human population growth are correct, however, present rice yields will be insufficient within a few years. Rice yields will have to increase by an estimated 60% in the next 30 years, or global food security will be in danger. The classical methods of previous green revolutions alone will probably not be able to meet this challenge, without being coupled to recombinant DNA technology. Here, we focus on the promise of these modern technologies in the area of nitrogen acquisition in rice, recognizing that nitrogen deficiency compromises the realization of rice yield potential in the field more than any other single factor. We summarize rice-specific advances in four key areas of research: (1) nitrogen fixation, (2) primary nitrogen acquisition, (3) manipulations of internal nitrogen metabolism, and (4) interactions between nitrogen and photosynthesis. We develop a model for future plant breeding possibilities, pointing out the importance of coming to terms with the complex interactions among the physiological components under manipulation, in the context of ensuring proper targeting of intellectual and financial resources in this crucial area of research. BioEssays 26:683,692, 2004. © 2004 Wiley Periodicals, Inc. [source] Crystallization and preliminary crystallographic characterization of glutamine synthetase from Medicago truncatulaACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 12 2009Ana Rita Seabra The condensation of ammonium and glutamate into glutamine catalyzed by glutamine synthetase (GS) is a fundamental step in nitrogen metabolism in all kingdoms of life. In plants, this is preceded by the reduction of inorganic nitrogen to an ammonium ion and therefore effectively articulates nitrogen fixation and metabolism. Although the three-dimensional structure of the dodecameric bacterial GS was determined quite some time ago, the quaternary architecture of the plant enzyme has long been assumed to be octameric, mostly on the basis of low-resolution electron-microscopy studies. Recently, the crystallographic structure of a monocotyledonous plant GS was reported that revealed a homodecameric organization. In order to unambiguously establish the quaternary architecture of GS from dicotyledonous plants, GS1a from the model legume Medicago truncatula was overexpressed, purified and crystallized. The collection of synchrotron diffraction data to 2.35,Å resolution allowed the determination of the three-dimensional structure of this enzyme by molecular replacement. [source] Differential expression of the genes involved in amino acids and nitrogen metabolisms during liver regeneration of miceHEPATOLOGY RESEARCH, Issue 3 2009Yunsheng Yuan Aim:, Liver regeneration is a highly coordinated response to hepatic injury or resection that is controlled by the body's overall requirement for liver function. The level of circulating amino acids in blood increases after acute liver injury and administration of amino acid mixtures induces hepatic DNA replication. These findings suggest a close connection between amino acid metabolism and hepatic proliferation. However, the underlying molecular mechanisms have not been completely elucidated. Here, we applied a cDNA micro-array technique to analyze expression profiles of the genes associated with nitrogen and amino acid metabolism during liver regeneration in mice following treatment with CCl4. Methods:, Seventy-nine genes were identified for their significantly altered expression patterns at different stages of liver damage and regeneration. Results:, We observed that the numbers of down-regulated genes were remarkably higher than that of up-regulated genes at 1.5 days following carbon tetrachloride administration when hepatic DNA replication was most active, indicating the existence of a counter balance between cell proliferation and liver metabolism functions. Conclusions:, Our results suggest that suppression of amino acids metabolism after acute liver injury results in the accumulation of amino acids in plasma that serves as a driving force for liver regeneration. [source] | |||||||||||||||||||||||||||||||