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Amino Acid Used (amino + acid_used)
Selected AbstractsCharging of tRNA with non-natural amino acids at high pressureFEBS JOURNAL, Issue 13 2006Malgorzata Giel-Pietraszuk We show a simple and reliable method of tRNA aminoacylation with natural, as well as non-natural, amino acids at high pressure. Such specific and noncognate tRNAs can be used as valuable substrates for protein engineering. Aminoacylation yield at high pressure depends on the chemical nature of the amino acid used and it is up to 10%. Using CoA, which carries two potentially reactive groups -SH and -OH, as a model compound we showed that at high pressure amino acid is bound preferentially to the hydroxyl group of the terminal ribose ring. [source] Stereoselective Aldol Reactions Catalyzed by Acyclic Amino Acids in Aqueous MicellesHELVETICA CHIMICA ACTA, Issue 1 2007Dong-Sheng Deng Abstract The catalytic properties of all proteinogenic, acyclic amino acids for direct aldol reaction in H2O, assisted by various surfactants, were investigated. The basic and neutral amino acids were shown to be efficient catalysts, giving rise to good-to-excellent yields of adducts (up to 95%), with moderate-to-good diastereoselectivities (up to 86%), L -arginine being the most-effective catalyst. The syn/anti diastereoisomer ratio could be readily tuned by proper choice of the amino acid used. Also, the range of substrates that underwent the reaction was extended to less-reactive aldehydes carrying electron-donating Br substituents. [source] Synthesis and specific biodegradation of novel polyesteramides containing amino acid residuesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2001Yujiang Fan Abstract Novel polyesteramides were synthesized from p -nitrophenyl esters of sebacic or adipic acids and diamines containing ,-amino acid ester groups. The optimal polymerization condition was 60 °C in N,N -dimethylformamide. The structures of these polymers were confirmed by IR and NMR. The number-average molecular weights of these polyesteramides ranged from 2280 to 23,600 (except for the polymers containing glycine residues), depending on the nature of the amino acid used. The biodegradability of the polyesteramides was investigated by in vitro hydrolysis with proteases and a lipase as catalysts in borate buffer solutions. The results indicated that the polymers containing L -phenylalanine were hydrolyzed most effectively by ,-chymotrypsin, subtilisin Carlsberg, and subtilisin BPN,. The polyesteramides containing other amino acid residues also underwent hydrolysis to different extents, reflecting the substrate specificity of the proteases. Lipase had almost no effect on the hydrolytic degradation of these polyesteramides. The polymers containing glycine residues were hardly decomposed by any of the enzymes used. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1318,1328, 2001 [source] Enantioselective Synthesis of l -Homophenylalanine by Whole Cells of Recombinant Escherichia coli Expressing l -Aminoacylase and N -Acylamino Acid Racemase Genes from Deinococcus radiodurans BCRC12827BIOTECHNOLOGY PROGRESS, Issue 6 2006Shih-Kuang Hsu l -Homophenylalanine (l -HPA) is a chiral unnatural amino acid used in the synthesis of angiotensin converting enzyme inhibitors and many pharmaceuticals. To develop a bioconversion process with dynamic resolution of N -acylamino acids for the l -HPA production, N -acylamino acid racemase (NAAAR) and l -aminoacylase (LAA) genes were cloned from Deinococcus radiodurans BCRC12827 and expressed in Escherichia coli XLIBlue. The recombinant enzymes were purified by nickel-chelate chromatography, and their biochemical properties were determined. The NAAAR had high racemization activity toward chiral N -acetyl-homophenylalanine (NAc-HPA). The LAA exhibited strict l -enantioselection to hydrolyze the NAc- l -HPA. A stirred glass vessel containing transformed E. coli cells expressing D. radiodurans NAAAR and LAA was used for the conversion of NAc- d -HPA to l -HPA. Unbalance activities of LAA and NAAAR were found in E. coli cell coexpressing laa and naaar genes, which resulted in the accumulation of an intermediate, NAc- l -HPA, in the early stage of conversion and a low productivity of 0.83 mmol l -HPA/L h. The results indicated that low activity of LAA present in the biomass is the rate-limiting factor in l -HPA production. In the case of two whole cells with separately expressed enzyme, the enzymatic activities of LAA and NAAAR could be balanced by changing the loading of individual cells. When the activities of two enzymes were fixed at 3600 U/L, 99.9% yield of l -HPA could be reached in 1 h, with a productivity of 10 mmol l -HPA/L h. The cells can be reused at least six cycles at a conversion yield of more than 96%. This is the first NAAAR/LAA process using NAc-HPA as substrate and recombinant whole cells containing Deinococcus enzymes as catalysts for the production of l -HPA to be reported. [source] Enantioselective Fluorescence Sensing of Amino Acids by Modified Cyclodextrins: Role of the Cavity and Sensing MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2004Sara Pagliari Dr. Abstract Two selectors based on modified cyclodextrins containing a metal binding site and a dansyl fluorophore,6-deoxy-6- N -(N, -[(5-dimethylamino-1-naphthalenesulfonyl)aminoethyl]phenylalanylamino-,-cyclodextrin,containing D -Phe (3) and L -Phe (4) moieties were synthesized. The conformations of the two selectors were studied by circular dichroism, two-dimensional NMR spectroscopy and time-resolved fluorescence spectroscopy. Cyclodextrin 4 was found to have a predominant conformation in which the dansyl group is self-included in the cyclodextrin cavity, while 3 showed a larger proportion of the conformation with the dansyl group outside the cavity. As a consequence, the two cyclodextrins were found to bind copper(II) with different affinities, as revealed by fluorescence quenching in competitive binding measurements. Addition of D - or L -amino acids induced increases in fluorescence intensity, which were dependent on the amino acid used and in some cases on its absolute configuration. The cyclodextrin 4 was found to be more enantioselective than 3, suggesting that the self-inclusion in the cyclodextrin cavity strongly increases the chiral discrimination ability of the copper(II) complex. Accordingly, a linear fluorescent ligand N, -[(5-dimethylamino-1-naphthalenesulfonyl)aminoethyl]- N1 -propyl-phenylalaninamide, which has the same binding site and absolute configuration as 4, showed very low chiral discrimination ability. The enantioselectivity in fluorescence response was found to be due to the formation of diastereomeric ternary complexes, which were detected by ESI-MS and by circular dichroism. Time-resolved fluorescence studies showed that the fluorescence of the dansyl group was completely quenched in the ternary complexes formed, and that the residual fluorescence was due to uncomplexed ligand. [source] |