|
| ||
|
|
||
Acid Precursors (acid + precursor)
Selected AbstractsPreparation of Ba6,3xNd8+2xTi18O54 via Ethylenediaminetetraacetic Acid PrecursorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000Yebin Xu Ba6,3xNd8+2xTi18O54 ceramic powders were synthesized by the modified Pechini method using ethylenediaminetetraacetic acid (EDTA) as a chelating agent. A purplish red, molecular-level, homogeneously mixed gel was prepared, and transferred into a porous resin intermediate through charring. Single-phase and well-crystallized Ba6,3xNd8+2xTi18O54 powders were obtained from pulverized resin at a temperature of 900°C for 3 h, without formation of any intermediate phases. Meanwhile, the molar ratio of EDTA to total metal cation concentration had a significant influence on the crystallization behavior of Ba6,3xNd8+2xTi18O54. The Ba6,3xNd8+2xTi18O54 (x= 2/3) ceramics prepared via EDTA precursor have excellent microwave dielectric characteristics: ,= 87, Qf= 8710 GHz. [source] Chronic acid ingestion promotes renal stone formation in rats treated with vitamin D3INTERNATIONAL JOURNAL OF UROLOGY, Issue 1 2007Naohiko Okamoto Objective: Although hypercalciuria, a well-established adverse effect of vitamin D3, can be a risk factor of renal stone formation, the risk of nephrolithiasis has not been well defined. The consumption of a diet high in acid precursors is often cited as a risk factor for the development of calcium-based kidney stones. In the present study, we investigated the effect of chronic acid ingestion on kidney stone formation in rats treated with calcitriol (1,25[OH]2 D3). Methods: Control rats (C-C), calcitriol-treated rats (C-V; three treatments of 0.5 µg of calcitriol per week) and acid-ingested (water containing 0.21 mol/L NH4Cl), calcitriol-treated (three treatments of 0.5 µg of calcitriol per week) rats (A-V) were fed in metabolic cages. After 1 month, urine, blood, kidney and bone samples were analyzed. Results: The A-V rats exhibited elevated serum calcium concentrations, urinary calcium and phosphate excretion, urinary type I collagen cross-linked N-peptide (NTx)/creatinine values, mRNA expression of osteopontin in the kidney, and renal calcium contents as well as decreased bone mineral densities, compared with the C-C and C-V rats. Urinary citrate excretion was lower and NaDC-1 mRNA expression in the kidney was higher in the A-V rats than in the C-C and C-V rats. Calcium phosphate kidney stones were found in the A-V rats. Conclusions: The ingestion of NH4Cl, an acid precursor, promotes calcium phosphate kidney stone formation in calcitriol-treated rats. The chronic intake of a diet rich in acid precursors may be a risk factor for the development of kidney stones in subjects who are being treated with calcitriol. [source] Highly efficient synthesis of [11C]S12968 and [11C]S12967, for the in vivo imaging of the cardiac calcium channels using PETJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 7 2001Frédéric Dolle Abstract The dihydrophyridines S12968 ((,)-S11568, absolute configuration S) and S12967 ((+)-S11568, absolute configuration R), 3-ethyl 5-methyl (,/+)-2-[(2-(2-aminoethoxy)ethoxy)methyl]-4-(2,3-dichlorophenyl)-6-methyl-1,4-dihydropyridine-3,5-dicarboxylate, have both an in vitro profile of high potency and of high selectivity for the low-voltage-dependent L-type calcium channel. In this paper, the radiosynthesis of both enantiomers, S12968 and S12967, with carbon-11, a positron-emitting isotope (half-life : 20.4 min) was investigated and oriented towards the preparation of multi milliCuries of radiotracer. Typically, 130,250 mCi (4.81,9.25 GBq) of [11C]S12968 and [11C]S12967 were obtained within 30 min of radiosynthesis (HPLC purification included) with specific radioactivities ranging from 500 to 1000 mCi/,mol (18.5,37.0 GBq/,mol) using no-carrier-added [11C]methyl triflate as the alkylating agent and the appropriate, enantiomerically pure carboxylic acid precursor at 100°C for 1 min. Based on preliminary PET experiments, only the levo enantiomer S12968 ((,)-[11C]-1) appears to be suitable for myocardial PET imaging as demonstrated in vivo in beagle dogs: with S12968, 85% of the uptake of [11C]S12968 could be inhibited in pretreatment experiments and up to 70% of [11C]S12968 could be displaced. Further investigations are currently underway in order to provide an absolute quantification of ventricular calcium channels with PET. Copyright © 2001 John Wiley & Sons, Ltd. [source] Synthesis of a model cyclic triblock terpolymer of styrene, isoprene, and methyl methacrylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2002Dimitris Pantazis Abstract The synthesis of a model cyclic triblock terpolymer [cyclic(S- b -I- b -MMA] of styrene (S), isoprene (I), and methyl methacrylate (MMA) was achieved by the end-to-end intramolecular amidation reaction of the corresponding linear ,,,-amino acid precursor [S- b -I- b -MMA] under high-dilution conditions. The linear precursor was synthesized by the sequential anionic polymerization of S, I, and MMA with 2,2,5,5-tetramethyl-1-(3-lithiopropyl)-1-aza-2,5-disilacyclopentane as an initiator and amine generator and 4-bromo-1,1,1-trimethoxybutane as a terminator and carboxylic acid generator. The separation of the unreacted linear polymer from the cyclic terpolymer was facilitated by the transformation of the unreacted species into high molecular weight polymers by the evaporation of the reaction solvent and the continuation of the reaction under high-concentration conditions. The intermediate materials and the final cyclic terpolymer, characterized by size exclusion chromatography, vapor pressure osmometry, thin-layer chromatography, IR and NMR spectroscopy, exhibited high molecular weight and compositional homogeneity. Dilute-solution viscosity measurements were used as an additional proof of the cyclic structure. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1476,1483, 2002 [source] Mechanism of membrane fluidity optimization: isothermal control of the Bacillus subtilis acyl-lipid desaturaseMOLECULAR MICROBIOLOGY, Issue 5 2002Larisa E. Cybulski Summary The Des pathway of Bacillus subtilis regulates the expression of the acyl-lipid desaturase, Des, thereby controlling the synthesis of unsaturated fatty acids (UFAs) from saturated phospholipid precursors. Previously, we showed that the master switch for the Des pathway is a two-component regulatory system composed of a membrane-associated kinase, DesK, and a soluble transcriptional regulator, DesR, which stringently controls transcription of the des gene. Activation of this pathway takes place when cells are shifted to low growth temperature. Here, we report on the mechanism by which isoleucine regulates the Des pathway. We found that exogenous isoleucine sources, as well as its ,-keto acid derivative, which is a branched-chain fatty acid precursor, negatively regulate the expression of the des gene at 37°C. The DesK,DesR two-component system mediates this response, as both partners are required to sense and transduce the isoleucine signal at 37°C. Fatty acid profiles strongly indicate that isoleucine affects the signalling state of the DesK sensor protein by dramatically increasing the incorporation of the lower-melting-point anteiso-branched-chain fatty acids into membrane phospholipids. We propose that both a decrease in membrane fluidity at constant temperature and a temperature downshift induce des by the same mechanism. Thus, the Des pathway would provide a novel mechanism to optimize membrane lipid fluidity at a constant temperature. [source] Current Progress in the Fatty Acid Metabolism in Cryptosporidium parvum,THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 4 2004GUAN ZHU ABSTRACT Cryptosporidium parvum is one of the apicomplexans that can cause severe diarrhea in humans and animals. The slow development of anti-cryptosporidiosis chemotherapy is primarily due to the poor understanding on the basic metabolic pathways in this parasite. Many well-defined or promising drug targets found in other apicomplexans are either absent or highly divergent in C. parvum. The recently discovered apicoplast and its associated Type n fatty acid synthetic enzymes in Plasmodium, Toxoplasma, and Eimeria apicomplexans are absent in C. parvum, suggesting this parasite is unable to synthesize fatty acids de novo. However, C. parvum possesses a giant Type I fatty acid synthase (CpFASl) that makes very long chain fatty acids using mediate or long chain fatty acids as precursors. Cryptosporidium also contains a Type I polyketide synthase (CpPKSl) that is probably involved in the production of unknown polyketide(s) from a fatty acid precursor. In addition to CpFASl and CpPKSl, a number of other enzymes involved in fatty acid metabolism have also been identified. These include a long chain fatty acyl elongase (LCE), a cytosolic acetyl-CoA carboxylase (ACCase), three acyl-CoA synthases (ACS), and an unusual "long-type" acyl-CoA binding protein (ACBP), which allows us to hypothetically reconstruct the highly streamlined fatty acid metabolism in this parasite. However, C. parvum lacks enzymes for the oxidation of fatty acids, indicating that fatty acids are not an energy source for this parasite. Since fatty acids are essential components of all biomembranes, molecular and functional studies on these critical enzymes would not only deepen our understanding on the basic metabolism in the parasites, but also point new directions for the drug discovery against C. parvum and other apicomplexan-based diseases. [source] Characterization of a dual specificity aryl acid adenylation enzyme with dual function in nikkomycin biosynthesisBIOPOLYMERS, Issue 9 2010Mary Moon Abstract Nikkomycin Z is a dipeptide antifungal antibiotic characterized by two nonproteinogenic amino acids, nikkomycin CZ and 4-(4,-hydroxy-2,-pyridinyl)-homothreonine (HPHT). The HPHT scaffold is assembled by an aldol reaction between 2-oxobutyrate and picolinaldehyde, the latter of which is derived from picolinic acid that is activated and loaded to coenzyme A by the aryl-activating adenylation enzyme, NikE. We now provide evidence that NikE is also involved in the activation and loading of the ,-keto acid precursor, 4-(2,-pyridinyl)-2-oxo-4-hydroxyisovalerate (POHIV), to a phosphopantetheinyl group of an acyl carrier protein domain of NikT. POHIV was synthesized using Escherichia coli 2-dehydro-3-deoxy-phosphogluconate aldolase, and phenylalanine dehydrogenase from Bacillus sp. NRRL B-14911 was used to prepare the ,-amino acid, 4-(2,-pyridinyl)-homothreonine (PHT). Using the carboxylic acid-dependent, ATP-[32P]PPi exchange assay, NikE is shown to activate both picolinic acid and POHIV but not PHT. Furthermore, NikE loads POHIV to holo-NikT to generate a new thioester-linked intermediate, which was not observed using a NikT(S33A) mutant. Thus, NikE activates two distinct carboxylic acids to form two new thioester intermediates, one of which is subsequently reduced to the aldehyde and the other that likely serves as a substrate for the aminotransferase domain of NikT prior to condensation with nikkomycin CZ to yield the dipeptide. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 791,801, 2010. [source] Enzymes involved in flavour formation by bacteria isolated from the smear population of surface-ripened cheeseINTERNATIONAL JOURNAL OF DAIRY TECHNOLOGY, Issue 1 2004A G Williams Twenty-five bacterial isolates recovered from the surface population of smear-ripened cheese were assigned phenotypically as Brevibacterium spp., Corynebacterium spp. and Aureobacterium spp. using the Biolog GP2 microplate system and database. The range and activity of hydrolytic enzymes involved in the formation of cheese flavour constituents were monitored in cell-free lysates of the isolates. Esterase activity and the presence of a range of enzymes involved in amino acid release and breakdown was confirmed in all strains examined although there were pronounced interspecies and strain differences in the level of activity detected. Peptidolytic activities present in the smear bacteria included dipeptidyl peptidase and aminopeptidases that cleaved various N-terminal amino acids including proline. Subsequent breakdown of the released aromatic and branched-chain amino acids was mediated by ,-keto acid dependent aminotransferase action and several of the isolates were able to form thiols from sulphur-containing amino acid precursors. It was confirmed that the enzymic activity of the smear population could be manipulated by the use of defined starter cultures comprising selected combinations of smear isolates. The hydrolytic activities of the smear bacteria are involved in the generation of cheese flavour compounds and the enzyme profile is thus an important selection criterion for strains to be evaluated for use in defined surface smear preparations. [source] Chronic acid ingestion promotes renal stone formation in rats treated with vitamin D3INTERNATIONAL JOURNAL OF UROLOGY, Issue 1 2007Naohiko Okamoto Objective: Although hypercalciuria, a well-established adverse effect of vitamin D3, can be a risk factor of renal stone formation, the risk of nephrolithiasis has not been well defined. The consumption of a diet high in acid precursors is often cited as a risk factor for the development of calcium-based kidney stones. In the present study, we investigated the effect of chronic acid ingestion on kidney stone formation in rats treated with calcitriol (1,25[OH]2 D3). Methods: Control rats (C-C), calcitriol-treated rats (C-V; three treatments of 0.5 µg of calcitriol per week) and acid-ingested (water containing 0.21 mol/L NH4Cl), calcitriol-treated (three treatments of 0.5 µg of calcitriol per week) rats (A-V) were fed in metabolic cages. After 1 month, urine, blood, kidney and bone samples were analyzed. Results: The A-V rats exhibited elevated serum calcium concentrations, urinary calcium and phosphate excretion, urinary type I collagen cross-linked N-peptide (NTx)/creatinine values, mRNA expression of osteopontin in the kidney, and renal calcium contents as well as decreased bone mineral densities, compared with the C-C and C-V rats. Urinary citrate excretion was lower and NaDC-1 mRNA expression in the kidney was higher in the A-V rats than in the C-C and C-V rats. Calcium phosphate kidney stones were found in the A-V rats. Conclusions: The ingestion of NH4Cl, an acid precursor, promotes calcium phosphate kidney stone formation in calcitriol-treated rats. The chronic intake of a diet rich in acid precursors may be a risk factor for the development of kidney stones in subjects who are being treated with calcitriol. [source] Penta-deuterated acid precursors in the pheromone biosynthesis of the Egyptian armyworm, Spodoptera littoralisJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 12 2009Lourdes Muñoz Abstract Synthesis of penta-deuterated intermediate precursors d5(E)-11-14:Acid (7), d5(Z)-11-14:Acid (10) and d514:Acid (12) of the pheromone of the Egyptian armyworm Spodoptera littoralis has been accomplished by a very convenient route starting from the commercially available 9-dodecyn-1-ol. The processes occur with a high to excellent chemical and stereochemical yields and the compounds have been successfully used in the confirmation of the pheromone composition and biosynthesis of our strain. Copyright © 2009 John Wiley & Sons, Ltd. [source] Lipoprotein Metabolism in Obesity and Diabetes: Insights from Stable Isotope Kinetic Studies in HumansNUTRITION REVIEWS, Issue 11 2003Julian B. Marsh MD The paradigm of obesity leading to insulin resistance and type 2 diabetes is examined in relation to dyslipidemia, which typically consists of high levels of triglycerides (TG) and low levels of high-density lipoprotein (HDL). Kinetic studies with stable isotope-labeled amino acid precursors have shown that the development of visceral obesity, as well as type 2 diabetes, leads to overproduction of the apolipoprotein B-100 and TG in very low- density lipoproteins. Elevated plasma levels or increased flux of albumin-bound free fatty acids to the liver appear to be underlying metabolic events in this process. Low levels of HDL are due to increased catabolism, which can be related to TG enrichment. [source] Influence of different phosphorus precursors on the electrical properties of the SiO2 -P2O5 films obtained by sol-gelPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2008Cristina Vasiliu Abstract This work aims at establishing the influence of different phosphor-precursors on the electrical properties of 90%SiO2 -10%P2O5 (%mol) thin films prepared by sol-gel method from triethylphosphate, triethylphosphite and phosphoric acid precursors. Glass and respectively ITO-coated glass were used as substrates. The films were annealed at 200 °C and respectively 500 °C. For all selected precursors the results show that the conduction in the phosphate glass films decreases with increasing annealing temperature, giving thus evidence of a reduced release- and transfer-activity of protons within the films. The activation energy of the conduction process takes values in the range 0.033-0.04 eV. The correlation between the electrical properties and optical and structural data is also discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatio-temporal expression of patatin-like lipid acyl hydrolases and accumulation of jasmonates in elicitor-treated tobacco leaves are not affected by endogenous levels of salicylic acidTHE PLANT JOURNAL, Issue 5 2002Sandrine Dhondt Summary We have previously isolated three tobacco genes (NtPat) encoding patatin-like proteins, getting rapidly induced during the hypersensitive response (HR) to tobacco mosaic virus, in advance to jasmonate accumulation. NtPAT enzymes are lipid acyl hydrolases that display high phospholipase A2 (PLA2) activity and may mobilize fatty acid precursors of oxylipins. Here, we performed a detailed study of NtPat gene regulation under various biotic and abiotic stresses. PLA2 activity was poorly induced in response to drought, wounding, reactive oxygen intermediates, salicylic acid (SA) or methyl-jasmonate (MJ) whereas the ethylene (ET) precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), provoked a moderate induction. In contrast, PLA2 activity was strongly induced when ACC was combined with MJ, and in response to the bacterium Erwinia carotovora or to the fungus Botrytis cinerea, as well as to treatment with ,-megaspermin, a cell death-inducing protein elicitor. A simplified system based on the infiltration of ,-megaspermin into leaves was used to dissect the spatio-temporal activation of PLA2 activity with regards to the accumulation of jasmonates and to the influence of endogenous SA. NtPat -encoded PLA2 activity was rapidly induced in the infiltrated zone before the appearance of cell death and with some delay in the surrounding living cells. A massive accumulation of 12-oxo-phytodienoic and jasmonic acids occurred in the elicitor-infiltrated zone, but only low levels were detectable outside this area. A similar picture was found in SA-deficient plants, showing that in tobacco, accumulation of jasmonates is not affected by the concomitant HR-induced build-up of endogenous SA. Finally, ET-insensitive plants showed a weakened induction of PLA2 activity outside the elicitor-infiltrated tissue. [source] The 1.9,Å structure of the branched-chain amino-acid transaminase (IlvE) from Mycobacterium tuberculosisACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 11 2009L. W. Tremblay Unlike mammals, bacteria encode enzymes that synthesize branched-chain amino acids. The pyridoxal 5,-phosphate-dependent transaminase performs the final biosynthetic step in these pathways, converting keto acid precursors into ,-amino acids. The branched-chain amino-acid transaminase from Mycobacterium tuberculosis (MtIlvE) has been crystallized and its structure has been solved at 1.9,Å resolution. The MtIlvE monomer is composed of two domains that interact to form the active site. The biologically active form of IlvE is a homodimer in which each monomer contributes a substrate-specificity loop to the partner molecule. Additional substrate selectivity may be imparted by a conserved N-terminal Phe30 residue, which has previously been observed to shield the active site in the type IV fold homodimer. The active site of MtIlvE contains density corresponding to bound PMP, which is likely to be a consequence of the presence of tryptone in the crystallization medium. Additionally, two cysteine residues are positioned at the dimer interface for disulfide-bond formation under oxidative conditions. It is unknown whether they are involved in any regulatory activities analogous to those of the human mitochondrial branched-chain amino-acid transaminase. [source] The role of Ureaplasma nucleoside monophosphate kinases in the synthesis of nucleoside triphosphatesFEBS JOURNAL, Issue 8 2007Liya Wang Mollicutes are wall-less bacteria and cause various diseases in humans, animals and plants. They have the smallest genomes with low G + C content and lack many genes of DNA, RNA and protein precursor biosynthesis. Nucleoside diphosphate kinase (NDK), a house-keeping enzyme that plays a critical role in the synthesis of nucleic acids precursors, i.e. NTPs and dNTPs, is absent in all the Mollicutes genomes sequenced to date. Therefore, it would be of interest to know how Mollicutes synthesize dNTPs/NTPs without NDK. To answer this question, nucleoside monophosphate kinases (NMPKs) from Ureaplasma were studied regarding their role in the synthesis of NTPs/dNTPs. In this work, Ureaplasma adenylate kinase, cytidylate kinase, uridylate kinase and thymidylate kinase were cloned and expressed in Escherichia coli. The recombinant enzymes were purified and characterized. These NMPKs are base specific, as indicated by their names, and capable of converting (d)NMPs directly to (d)NTPs. The catalytic rates of (d)NTPs and (d)NDP synthesis by these NMPKs were determined using tritium-labelled (d)NMPs, and the rates for (d)NDP synthesis, in general, were much higher (up to 100-fold) than that of (d)NTP. Equilibrium studies with adenylate kinase suggested that the rates of NTPs/dNTPs synthesis by NMPKs in vivo are probably regulated by the levels of (d)NMPs. These results strongly indicate that NMPKs could substitute the NDK function in vivo. [source] | |||||||||||||||||||