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Amino Acid Biosynthesis (amino + acid_biosynthesis)
Selected AbstractsRegulation of branched-chain amino acid biosynthesis by ,-acetolactate decarboxylase in Streptococcus thermophilusLETTERS IN APPLIED MICROBIOLOGY, Issue 6 2003C. Monnet Abstract Aims: To demonstrate the presence of an active , -acetolactate decarboxylase in Streptococcus thermophilus and to investigate its physiological function. Methods and Results:Streptococcus thermophilus CNRZ385 contains a gene encoding an , -acetolactate decarboxylase. Comparison of the production of , -acetolactate and its decarboxylation products, by the parent strain and an , -acetolactate decarboxylase-deficient mutant, demonstrated the presence of a control of the pool of ,-acetolactate by valine, leucine and isoleucine. This control occurs via an allosteric activation of the , -acetolactate decarboxylase. Cell-free extracts of S. thermophilus were not able to decarboxylate the isoleucine precursor , -acetohydroxybutyrate. Conclusions: These results strongly suggest that one of the physiological functions of the , -acetolactate decarboxylase in S. thermophilus is to regulate leucine and valine biosynthesis by diverting the flux of , -acetolactate towards acetoin when the branched-chain amino acids are present at a high concentration. Significance and Impact of the Study: Regulation of branched-chain amino acid biosynthesis by , -acetolactate decarboxylase may occur in several other micro-organisms and explain some of their growth properties. [source] A dimeric 5- enol -pyruvyl-shikimate-3-phosphate synthase from the cyanobacterium Spirulina platensisNEW PHYTOLOGIST, Issue 2 2001Giuseppe Forlani Summary ,,Isolation and biochemical characterization is reported here of 5- enol -pyruvyl-shikimate-3-phosphate (EPSP) synthase, the enzyme that catalyses the sixth step in the common prechorismate pathway of aromatic amino acid biosynthesis and the target of the widely used herbicide glyphosate, from the cyanobacterium Spirulina platensis. ,,Homogeneous enzyme preparations were obtained by ammonium sulphate fractionation, anion-exchange and substrate-elution chromatography, and chromatofocusing. Protein characterization was carried out by conventional kinetic analysis, PAGE and gel permeation. ,,A 2800-fold purification was achieved, with a recovery of 20% of initial activity. Unusually low apparent affinities for both substrates, phosphoenolpyruvate and shikimate-3-phosphate, did not correspond to decreased glyphosate sensitivity. During SDS-PAGE, the protein migrated as a single band corresponding to a molecular mass of c. 49 kDa. The behaviour of the protein upon gel permeation chromatography under nondenaturing conditions was, however, consistent with a mass of c. 91 kDa. ,,The native enzyme appears to be homodimeric, a remarkable feature that has not been previously reported for EPSP synthases from either cyanobacteria or higher plants. The presence of mono- and dimeric EPSP synthases could represent an important tool for cyanobacterial classification. [source] The effect of low pH on protein expression by the probiotic bacterium Lactobacillus reuteriPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 8 2008KiBeom Lee Dr. Abstract The ability of a lactic acid bacterium to survive passage through the gastrointestinal tract is a key point in its function as a probiotic. In this study, protein synthesis by the probiotic bacterium, Lactobacillus reuteri, was analyzed under transiently decreased pH conditions. L. reuteri cells grown to the midexponential growth phase at 37°C were exposed to transient (1,h) low-pH stresses from pH,6.8 to pH,5.0, 4.5, or 4.0. 2-DE allowed us to identify 40 common proteins that were consistently and significantly altered under all three low-pH conditions. PMF was used to identify these 40 proteins, and functional annotation allowed them to be distributed to six major classes: (i) transport and binding proteins; (ii) transcription,translation; (iii) nucleotide metabolism and amino acid biosynthesis; (iv) carbon energy metabolism; (v) pH homeostasis and stress; and (vi) unassigned. These findings provide new insight into the inducible mechanisms underlying the capacity of gastrointestinal L. reuteri to tolerate acid stress. [source] Reduced amino acid content in transgenic potato tubers due to antisense inhibition of the leaf H+/amino acid symporter StAAP1THE PLANT JOURNAL, Issue 2 2003Wolfgang Koch Summary Transport processes across the plasma membrane of leaf vascular tissue are essential for transport and distribution of assimilates. In potato, leaves are the predominant sites for nitrate reduction and amino acid biosynthesis. From there, assimilated amino acids are exported through the phloem to supply tubers with organic nitrogen. To study the role of amino acid transporters in long-distance transport and allocation of organic nitrogen in potato plants, a gene encoding a functional, leaf-expressed amino acid permease StAAP1 was isolated. Similar to the sucrose transporter SUT1, StAAP1 expression was induced during the sink-to-source transition, indicating a role in phloem loading. To test the role of StAAP1, expression was inhibited by an antisense approach. Transgenic plants with reduced StAAP1 expression were phenotypically indistinguishable from wild type, as were photosynthetic capacity and tuber yield. However, tubers from antisense StAAP1 plants showed up to 50% reduction in free amino acid contents. In comparison, starch content was not affected or tended to increase relative to wild type. The reduction in all amino acids except aspartate in the antisense plants is consistent with the properties of amino acid permeases (AAPs) found in heterologous systems. The results demonstrate an important role for StAAP1 in long-distance transport of amino acids and highlight the importance of plasma membrane transport for nutrient distribution in plants. [source] Reciprocal 13C-Labeling: A Method for Investigating the Catabolism of CosubstratesBIOTECHNOLOGY PROGRESS, Issue 2 2002Bjarke Christensen The principle of reciprocal labeling is to use a uniformly 13C-labeled substrate as the primary carbon source and a naturally labeled cosubstrate. Metabolites derived from a naturally labeled cosubstrate, in this case amino acids, can then be identified by their relatively lower content of 13C, and information on the degradation pathway can be deduced. The technique is based on GC,MS measurements of amino acid labeling patterns, making the technique well suited for investigating the relative importance of amino acid biosynthesis and amino acid uptake from the medium, as the 13C content of the amino acids incorporated into biomass is a direct measure of the amino acid biosyntheses. The technique is illustrated by the investigation of the degradation of phenoxyacetic acid, a medium component that is essential for production of penicillin V by Penicillium chrysogenum. Glucose was used as the uniformly labeled primary carbon source. [source] Microreview: Type IV secretion in the obligatory intracellular bacterium Anaplasma phagocytophilumCELLULAR MICROBIOLOGY, Issue 9 2010Yasuko Rikihisa Summary Anaplasma phagocytophilum is an obligatory intracellular bacterium that infects neutrophils, the primary host defence cells. Consequent effects of infection on host cells result in a potentially fatal systemic disease called human granulocytic anaplasmosis. Despite ongoing reductive genome evolution and deletion of most genes for intermediary metabolism and amino acid biosynthesis, Anaplasma has also experienced expansion of genes encoding several components of the type IV secretion (T4S) apparatus. Two A. phagocytophilum T4S effector molecules are currently known; Anaplasma translocated substrate 1 (Ats-1) and ankyrin repeat domain-containing protein A (AnkA) have C-terminal positively charged amino acid residues that are recognized by the T4S coupling protein, VirD4. AnkA and Ats-1 contain eukaryotic protein motifs and are uniquely evolved in the family Anaplasmataceae; Ats-1 contains a mitochondria-targeting signal. They are abundantly produced and secreted into the host cytoplasm, are not toxic to host cells, and manipulate host cell processes to aid in the infection process. At the cellular level, the two effectors have distinct subcellular localization and signalling in host cells. Thus in this obligatory intracellular pathogen, the T4S system has evolved as a host-subversive survival factor. [source] | ||||||||||