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1.
Summary. To mutant ddY/DAO− mice lacking D-amino-acid oxidase activity and normal ddY/DAO+ mice, five D-amino acids (D-Asp, D-Ser, D-Ala, D-Leu and D-Pro) were orally administered for two weeks, and the D-amino acid levels were examined in seven brain regions. The levels of D-Asp markedly increased in the pituitary and pineal glands in both strains. In the ddY/DAO+ mice, the levels of the other D-amino acids did not significantly change in most of the brain regions. While in the ddY/DAO− mice the levels of D-Ser significantly increased in most of the brain regions except for the cerebrum and hippocampus. The levels of D-Ala and D-Leu increased in all regions but the levels of D-Pro did not significantly change. The same five D-amino acids were intravenously injected into Wistar rats and the D-amino acid levels in their brains were examined for 60 min after the administration. The levels of D-Asp markedly increased in the pineal gland 3 min after the administration, while the levels of D-Ser, D-Ala, and D-Pro increased both in the pineal and pituitary glands, the levels of D-Leu increased in all brain regions. These results are useful for the elucidation of the origins and regulation of D-amino acids in the mammalian body. 相似文献
2.
T. Ohshiro M. Shinji Y. Morita Y. Takayama Y. Izumi 《Applied microbiology and biotechnology》1997,48(4):546-548
Microorganisms capable of cleaving the urethane bond of t-butoxycarbonyl (Boc) amino acids in a whole-cell reaction were screened among stock cultures, and Corynebacterium aquaticum IFO12154 was the most promising. The conversion of Boc-Ala to Ala was stimulated by CoSO4 in the medium and reaction mixture. The optimum whole-cell concentration was 25 mg lyophilized cells/ml. Boc-l-Met was the best substrate for this reaction, and other Boc-L-amino acids, as well as benzyloxycarbonyl-l-amino acids with hydrophobic residues, were also good substrates. Boc-d- and Z-d-amino acids were inert. When the reactions had proceeded for 24 h with each substrate at 10 mM, the molar conversion rates
from Boc-l-, dl- and d-Met were 100%, 50%, and 0% respectively. From 150 mM Boc-l-Met, 143 mM l-Met was formed at a molar yield of 95.3%.
Received: 3 September 1996 / Received last revision: 7 April 1997 / Accepted: 19 April 1997 相似文献
3.
The d-enantiomers of proteinogenic amino acids fulfill essential functions in bacteria, fungi and animals. Just in the plant kingdom,
the metabolism and role of d-amino acids (d-AAs) still remains unclear, although plants have to cope with significant amounts of these compounds from microbial decay
in the rhizosphere. To fill this gap of knowledge, we tested the inhibitory effects of d-AAs on plant growth and established a method to quantitate 16 out of 19 proteinogenic amino acids and their d-enantiomers in plant tissue extracts. Therefore, the amino acids in the extracts were derivatized with Marfey’s reagent and
separated by HPLC–MS. We used two ecotypes (Col-0 and C24) and a mutant (lht1) of the model plant Arabidopsis thaliana to determine the influence and fate of exogenously applied d-AAs. All of them were found in high concentrations in the plant extracts after application, even in lht1, which points to additional transporters facilitating the import of d-AAs. The addition of particular amino acids (d-Trp, d-Phe, d-Met and d-His) led to the accumulation of the corresponding l-amino acid. In almost all cases, the application of a d-AA resulted in the accumulation of d-Ala and d-Glu. The presented results indicate that soil borne d-AAs can actively be taken up and metabolized via central metabolic routes. 相似文献
4.
Chang-Su Park Soo-Jin Yeom Yu-Ri Lim Yeong-Su Kim Deok-Kun Oh 《World journal of microbiology & biotechnology》2011,27(4):743-750
A putative ribose-5-phosphate isomerase (RpiB) from Streptococcus pneumoniae was purified with a specific activity of 26.7 U mg−1 by Hi-Trap Q HP anion exchange and Sephacryl S-300 HR 16/60 gel filtration chromatographies. The native enzyme existed as
a 96-kDa tetramer with activity maxima at pH 7.5 and 35°C. The RpiB exhibited isomerization activity with l-lyxose, l-talose, d-gulose, d-ribose, l-mannose, d-allose, l-xylulose, l-tagatose, d-sorbose, d-ribulose, l-fructose, and d-psicose and exhibited particularly high activity with l-form monosaccharides such as l-lyxose, l-xylulose, l-talose, and l-tagatose. With l-xylulose (500 g l−1) and l-talose (500 g l−1) substrates, the optimum concentrations of RpiB were 300 and 600 U ml−1, respectively. The enzyme converted 500 g l−1
l-xylulose to 350 g l−1
l-lyxose after 3 h, and yielded 450 g l−1
l-tagatose from 500 g l−1
l-talose after 5 h. These results suggest that RpiB from S. pneumoniae can be employed as a potential producer of l-form monosaccharides. 相似文献
5.
Saeed Zahmatkesh 《Amino acids》2011,40(2):533-542
N,N′-Pyromelliticdiimido-di-l-alanine (1), N,N′-Pyromelliticdiimido-di-l-phenylalanine (2), and N,N′-Pyromelliticdiimido-di-l-leucine (3) were prepared from the reaction of Pyromellitic dianhydride with corresponding l-amino acids in a mixture of glacial acetic acid and pyridine solution (3/2 ratio) under refluxing conditions. A series of
poly (amide-imide)s containing l-amino acids were prepared from the synthesized dicarboxylic acids with two synthetic aromatic diamines in an ionic liquid
(IL) as a green, safe and eco-friendly medium and also reactions catalysis agent. Evaluation of data shows that IL is the better polyamidation medium than the reported method and the catalysis stand on the higher inherent viscosities of
the obtained PAIs and the rate of polymerizations beyond the greener reaction conditions and deletion of some essential reagents in conventional
manners. Characterization were performs by means of IR, MS and 1H NMR spectroscopy, elemental analysis, specific rotation, thermogravimetric analysis and differential scanning calorimetric
techniques. Molecular weights of the obtained polymers were evaluated viscometrically, and the measured inherent viscosities
were in the range 0.43–0.85 dL/g. These polymers were readily soluble in many organic solvents. These polymers still kept
good thermal stability with glass transition temperatures in the range of 94–154°C, and the decomposition temperature under
the nitrogen atmosphere for 10% weight-loss temperatures in excess of 308°C. 相似文献
6.
Vidal L Calveras J Clapés P Ferrer P Caminal G 《Applied microbiology and biotechnology》2005,68(4):489-497
The glyA gene encoding a serine hydroxymethyl transferase (SHMT) with threonine aldolase activity was isolated from Streptococcus thermophilus YKA-184 chromosomal DNA. This aldolase is a pyridoxal 5′-phosphate-dependent enzyme that stereospecifically catalyzes the
interconversion of l-threonine to glycine and acetaldehyde. The enzyme was overexpressed in Escherichia coli M15 as a recombinant protein of 45 kDa with a His6-tag at its N-terminus. The recombinant enzyme was purified to homogeneity
by a single chromatographic step using Ni-nitrilotriacetic acid affinity, obtaining a high activity-recovery yield (83%).
Lyophilized and precipitated enzymes were stable at least for 10 weeks when stored at −20°C and 4°C. It was observed that
the K
m for l-allo-threonine was 38-fold higher than that for l-threonine, suggesting this enzyme can be classified as a specific l-allo-threonine aldolase. The optimum pH range of threonine aldolase activity for the recombinant SHMT was pH 6–7. When tested
for aldol addition reactions with non-natural aldehydes, such as benzyloxyacetaldehyde and (R)-N-Cbz-alaninal, two possible β-hydroxy-α-amino acid diastereoisomers were produced, but with moderate stereospecificity. The
enzyme showed potential as a biocatalyst for the stereoselective synthesis of β-hydroxy-α-amino acids. 相似文献
7.
An DS Cui CH Sung BH Yang HC Kim SC Lee ST Im WT Kim SG 《Applied microbiology and biotechnology》2012,94(3):673-682
The gene encoding an α-l-arabinofuranosidase that could biotransform ginsenoside Rc {3-O-[β-d-glucopyranosyl-(1–2)-β-d-glucopyranosyl]-20-O-[α-l-arabinofuranosyl-(1–6)-β-d-glucopyranosyl]-20(S)-protopanaxadiol} to ginsenoside Rd {3-O-[β-d-glucopyranosyl-(1–2)-β-d-glucopyranosyl]-20-O-β-d-glucopyranosyl-20(S)-protopanaxadiol} was cloned from a soil bacterium, Rhodanobacter ginsenosidimutans strain Gsoil 3054T, and the recombinant enzyme was characterized. The enzyme (AbfA) hydrolyzed the arabinofuranosyl moiety from ginsenoside
Rc and was classified as a family 51 glycoside hydrolase based on amino acid sequence analysis. Recombinant AbfA expressed
in Escherichia coli hydrolyzed non-reducing arabinofuranoside moieties with apparent K
m values of 0.53 ± 0.07 and 0.30 ± 0.07 mM and V
max values of 27.1 ± 1.7 and 49.6 ± 4.1 μmol min−1 mg−1 of protein for p-nitrophenyl-α-l-arabinofuranoside and ginsenoside Rc, respectively. The enzyme exhibited preferential substrate specificity of the exo-type
mode of action towards polyarabinosides or oligoarabinosides. AbfA demonstrated substrate-specific activity for the bioconversion
of ginsenosides, as it hydrolyzed only arabinofuranoside moieties from ginsenoside Rc and its derivatives, and not other sugar
groups. These results are the first report of a glycoside hydrolase family 51 α-l-arabinofuranosidase that can transform ginsenoside Rc to Rd. 相似文献
8.
J. Custot Jean-Luc Boucher Sandrine Vadon Catherine Guedes Sylvie Dijols Marcel Delaforge Daniel Mansuy 《Journal of biological inorganic chemistry》1996,1(1):73-82
The effects of various compounds bearing an N-OH group such as N-hydroxy-guanidines, amidoximes, and hydroxylamines, on bovine and rat liver arginases was studied. Some of these compounds
with an l-α-amino acid function at an appropriate distance from the N-OH group acted as strong competitive liver arginase inhibitors,
displaying Ki values between 4 and 150 μM. Two compounds, N
ε-hydroxy-l-lysine and N
ω-hydroxy-d,l-indospicine, which exhibited Ki values of 4 and 20 μM (at pH 7.4), were the most potent inhibitors of arginase described
to date. The distance between the α-amino acid and N-OH functions appeared to be crucial for potent inhibition of arginase,
as N
δ-hydroxy-l-ornithine, which has one -CH2 group less than N
ε-hydroxy-l-lysine, exhibited a 37-fold higher Ki value than N
ε-hydroxy-l-lysine. Based on these results, a model for the interaction of N
ω-hydroxyamino-l-α-amino acids with the arginase active site is proposed. This model involves the binding of the N-OH group of the inhibitors
to the arginase Mn(II) center and suggests that N
ε-hydroxy-l-lysine is a good transition state analog of arginase. 相似文献
9.
Based on the report that the introduction of the biosynthetic precursor of lincomycin, propylproline, could increase the production
of lincomycin (Bruce et al. in US Patent 3,753,859, 1973), a mutant strain pro10–20, with resistance of feedback suppression of proline (an analog of propylproline) was thus selected
and lincomycin production increased by 10%. The addition of three amino acids (l-proline, l-tyrosine, l-alanine) which are the precursors of propylproline to the fermentation medium was found to enhance the accumulation of l-dopa through different pathways and was favorable to lincomycin biosynthesis. The production of lincomycin was increased
by 23, 10, 13%, respectively, with the addition of 0.05 g L−1
l-proline at 60 h, 0.005 g L−1
l-tyrosine and 0.1 g L−1
l-alanine directly in the medium. 相似文献
10.
Yeasts that ferment both hexose and pentose are important for cost-effective ethanol production. We found that the soil yeast
strain NY7122 isolated from a blueberry field in Tsukuba (East Japan) could ferment both hexose and pentose (d-xylose and l-arabinose). NY7122 was closely related to Candida subhashii on the basis of the results of molecular identification using the sequence in the D1/D2 domains of 26S rDNA and 5.8S-internal
transcribed spacer region. NY7122 produced at least 7.40 and 3.86 g l−1 ethanol from 20 g l−1
d-xylose and l-arabinose within 24 h. NY7122 could produce ethanol from pentose and hexose sugars at 37°C. The highest ethanol productivity
of NY7122 was achieved under a low pH condition (pH 3.5). Fermentation of mixed sugars (50 g l−1 glucose, 20 g l−1
d-xylose, and 10 g l−1
l-arabinose) resulted in a maximum ethanol concentration of 27.3 g l−1 for the NY7122 strain versus 25.1 g l−1 for Scheffersomyces stipitis. This is the first study to report that Candida sp. NY7122 from a soil environment could produce ethanol from both d-xylose and l-arabinose. 相似文献
11.
Zusammenfassung Von L. plantarum und L. inulinus wurden die Zellwände isoliert und durch Inkubation mit Trypsin gereinigt. Durch Extraktion mit TES und Formamid konnte das Murein (Peptidoglycan) bis zu rund 85% der Trockenmasse angereichert werden. Die Zellwände von L. plantarum enthielten rund 30% Teichonsäure des Ribit-Typs, die von L. inulinus waren frei von Teichonsäure.Im Hydrolysat der teichonsäurefreien Zellwände ergaben sich folgende aufbzw. abgerundete Molverhältnisse Mur: GlNH2:Glu:DAPl-Alad-Ala=1:1:1:1:1:0,5. Außerdem waren 2 Mole Ammoniak enthalten, was das Vorliegen von Glu und DAP als Amide anzeigt. Die durch Hemmung mit d-Cycloserin angereicherte unvollständige Mureinvorstufe hatte ein Molverhältnis von UDP:Murl-Ala:Glu:DAP=1:1:1:1:1.Nach Dinitrophenylierung der Zellwand ließen sich rund 50% der gesamten DAP als mono-DNP-DAP nachweisen. Die Hydrazinolyse der Zellwand zum Nachweis C-terminaler Aminosäuren ergab 4% freies DAP und 0,8% freies Alanin.Durch die Analyse der in Partialhydrolysaten der Zellwand auftretenden Peptide konnte die folgende Aminosäuresequenz des an die Muraminsäure gebundenen Tetrapeptides bestimmt werden: l-Ala-d-Glu-l-Lys-d-Ala. Im Murein ist vermutlich nur etwa die Hälfte der Muraminsäure mit einem Tetrapeptid, die andere Hälfte mit einem Tripeptid, dessen d-Alanin fehlt, substituiert.Die Quervernetzung erfolgt zwischen der 2. Aminogruppe der DAP und der Carboxylgruppe des d-Alanins eines benachbarten Tetrapeptids.
The amino acid sequence of the DAP-containing murein of Lactobacillus plantarum and Lactobacillus inulinus
Summary Cell walls of L. plantarum and L. inulinus were isolated and purified by incubation with trypsin. After extraction with TCA and formamide, 85% of the dry weight consists of murein (peptidoglycan).The cell walls of L. plantarum contained about 30% teichoic acid (ribit-type), whereas no teichoic acid was present in the cell walls of L. inulinus.The quantitative determination of amino sugars and amino acids in the hydrolysate of the cell walls showed the following molar ratios: Mur: Gl-NH2:Glu:DAP l-Alad-Ala=1:1:1:1:1:0.5. In addition, 2 mols of NH3 were found per mol of glutamic acid, indicating, that DAP as well as glutamic acid are present as amides.The UDP-activated cell wall precursor which was accumulated by inhibiting the cells by d-cycloserine showed the following molar ratios: UDP:Murl-Ala: Glu:DAP=1:1:1:1:1.After dinitrophenylation and hydrolysation of the cell wall 50% of the DAP were present as mono-DNP-DAP. Hydrozinolysis of the cell wall yielded 4% free DAP and 0.8% free alanine. This shows that only a very small amount of these amino acids are C-terminal in the whole murein.The analysis of various peptides from acid partial hydrolysates of the cell wall indicates the following amino acid sequence of the tetrapeptides attached to muramic acid: l-Ala-d-Glu-meso-DAP-d-Ala. Only half of the muramic acid molecules are substituted by tetrapeptides, while the other half carries a tripeptide in which the terminal d-alanine is missing.The cross-linking of the muropeptides is achieved by a peptide-bond between the second amino group of DAP and the carboxylgroup of the d-alanine of an adjacent muropeptide.相似文献
12.
Broad specificity amino acid racemase (E.C. 5.1.1.10) from Pseudomonas putida IFO 12996 (BAR) is a unique racemase because of its broad substrate specificity. BAR has been considered as a possible catalyst
which directly converts inexpensive l-amino acids to dl-amino acid racemates. The gene encoding BAR was cloned to utilize BAR for the synthesis of d-amino acids, especially d-Trp which is an important intermediate of pharmaceuticals. The substrate specificity of cloned BAR covered all of the standard
amino acids; however, the activity toward Trp was low. Then, we performed random mutagenesis on bar to obtain mutant BAR derivatives with high activity for Trp. Five positive mutants were isolated after the two-step screening
of the randomly mutated BAR. After the determination of the amino acid substitutions in these mutants, it was suggested that
the substitutions at Y396 and I384 increased the Trp specific racemization activity and the racemization activity for overall
amino acids, respectively. Among the positive mutants, I384M mutant BAR showed the highest activity for Trp. l-Trp (20 mM) was successfully racemized, and the proportion of d-Trp was reached 43% using I384M mutant BAR, while wild-type BAR racemized only 6% of initial l-Trp. 相似文献
13.
Minoru Tanigawa Tomomitsu Shinohara Makoto Saito Katsushi Nishimura Yuichiro Hasegawa Sadao Wakabayashi Morio Ishizuka Yoko Nagata 《Amino acids》2010,38(1):247-255
Helicobacter pylori is a microaerophilic bacterium, associated with gastric inflammation and peptic ulcers. d-Amino acid dehydrogenase is a flavoenzyme that digests free neutral d-amino acids yielding corresponding 2-oxo acids and hydrogen. We sequenced the H. pylori NCTC 11637 d-amino acid dehydrogenase gene, dadA. The primary structure deduced from the gene showed low similarity with other bacterial d-amino acid dehydrogenases. We purified the enzyme to homogeneity from recombinant Escherichia coli cells by cloning dadA. The recombinant protein, DadA, with 44 kDa molecular mass, possessed FAD as cofactor, and showed the highest activity to
d-proline. The enzyme mediated electron transport from d-proline to coenzyme Q1, thus distinguishing it from d-amino acid oxidase. The apparent K
m and V
max values were 40.2 mM and 25.0 μmol min−1 mg−1, respectively, for dehydrogenation of d-proline, and were 8.2 μM and 12.3 μmol min−1 mg−1, respectively, for reduction of Q1. The respective pH and temperature optima were 8.0 and 37°C. Enzyme activity was inhibited markedly by benzoate, and moderately
by SH reagents. DadA showed more similarity with mammalian d-amino acid oxidase than other bacterial d-amino acid dehydrogenases in some enzymatic characteristics. Electron transport from d-proline to a c-type cytochrome was suggested spectrophotometrically. 相似文献
14.
Gen-Hai Zhao Hui Li Wei Liu Wei-Guo Zhang Fei Zhang Qian Liu Qing-Cai Jiao 《Amino acids》2011,40(1):215-220
In this research, an improved method for preparation of optically pure β-hydroxy-α-amino acids, catalyzed by serine hydroxymethyl
transferase with threonine aldolase activity, is reported. Using recombinant serine hydroxymethyl transferase (SHMT), an enzymatic
resolution process was established. A series of new substrates, β-phenylserine, β-(nitrophenyl) serine and β-(methylsulfonylphenyl)
serine were used in the resolution process catalyzed by immobilized Escherichia coli cells with SHMT activity. It was observed that the K
m for l-threonine was 28-fold higher than that for l-allo-threonine, suggesting that this enzyme can be classified as a low-specificity l-allo-threonine aldolase. The results also shows that SHMT activity with β-phenylserine as substrate was about 1.48-fold and 1.25-fold
higher than that with β-(methylsulfonylphenyl) serine and β-(nitrophenyl) serine as substrate, respectively. Reaction conditions
were optimized by using 200 mmol/l β-hydroxy-α-amino acid, and 0.1 g/ml of immobilized SHMT cells at pH 7.5 and 45°C. Under
these conditions, the immobilized cells were continuously used 10 times, yielding an average conversion rate of 60.4%. Bead
activity did not change significantly the first five times they were used, and the average conversion rate during the first
five instances was 84.1%. The immobilized cells exhibited favourable operational stability. 相似文献
15.
J. Ogawa A. Ryono S. -X. Xie R. M. Vohra R. Indrati H. Miyakawa T. Ueno Y. Ikenaka H. Nanba S. Takahashi S. Shimizu 《Applied microbiology and biotechnology》1999,52(6):797-801
N-Carbamoyl-d-α-amino acid amidohydrolase (d-carbamoylase) was found to distinguish stereochemistry not only at the α-carbon but also at the β-carbon of N-carbamoyl-d-α-amino acids. The enzyme selectively acted on one of the four stereoisomers of N-carbamoyl-α,β-diastereomeric amino acids. This simultaneous recognition of two chiral centers by d-carbamoylase was useful for the fine stereoselective synthesis of α,β-diastereomeric amino acids such as threonine, isoleucine,
3,4-methylenedioxyphenylserine and β-methylphenylalanine. The stereoselectivity for the β-carbon was influenced by the pH
of the reaction mixture and by the bulk of the substituent at the β-carbon.
Received: 18 June 1999 / Received revision: 30 July 1999 / Accepted: 6 August 1999 相似文献
16.
Paula Alayón-Luaces Eduardo A. Pagano Luis A. Mroginski Gabriel O. Sozzi 《Plant Cell, Tissue and Organ Culture》2008,95(3):257-263
α-l-Arabinofuranosidase, α- and β-d-xylosidase, and β-d-glucosidase activity was detected in the soluble fraction (S-F) extracted with water and in the NaCl-released fraction (NaCl-F)
extracted with a high-salt concentration buffer from apple callus cultures. The activity was found to be differentially modulated
by the addition of various plant growth regulators (PGRs) to calluses that had lost their requirement for specific PGRs (“habituation”
phenomenon). α-l-Arabinofuranosidase activity was 93%, 130%, 126% and 186% higher in the NaCl-F from IAA-, IBA-, ABA- and GA3-treated callus than in that extracted from untreated callus while S-F α-l-arabinofuranosidase activity was only 71%, 24%, 55% and 66% higher, respectively. α-d-Xylosidase displayed low activity levels in both S-F and NaCl-F but 2iP-treated callus showed higher α-d-xylosidase activity in both fractions than the control. 2,4-D increased α-d-xylosidase activity by 110% in the NaCl-F but decreased it by 40% in the S-F. β-d-Xylosidase activity increased by 99% in S-F from 2iP-treated callus but slightly decreased in the NaCl-F. In GA3-treated callus, NaCl-F β-d-xylosidase activity increased by 188%. S-F and NaCl-F from Picloram-treated callus showed undetectable or only slightly noticeable
α-l-arabinofuranosidase, α-d-xylosidase and β-d-xylosidase activity. Interestingly, β-d-glucosidase activity rose 28-fold in the S-F extracted from Picloram-treated callus. β-d-glucosidase was the only enzyme assayed that greatly increased its NaCl-F activity after 10 subcultures, and the addition
of any PGR to the callus culture –except for Picloram and ABA– decreased its activity, suggesting that this enzyme may be
associated with certain stress conditions, such as PGR starvation or Picloram addition. This is the first report on glycoside
hydrolases from fruit callus as modulated by different PGRs. 相似文献
17.
Jordan DB Wagschal K Fan Z Yuan L Braker JD Heng C 《Journal of industrial microbiology & biotechnology》2011,38(11):1821-1835
β-d-Xylosidase/α-l-arabinofuranosidase from Selenomonas ruminantium is the most active enzyme reported for catalyzing hydrolysis of 1,4-β-d-xylooligosaccharides to d-xylose. One property that could use improvement is its relatively high affinities for d-glucose and d-xylose (K
i ~ 10 mM), which would impede its performance as a catalyst in the saccharification of lignocellulosic biomass for the production
of biofuels and other value-added products. Previously, we discovered that the W145G variant expresses K
i
d-glucose and K
i
d-xylose twofold and threefold those of the wild-type enzyme. However, in comparison to the wild type, the variant expresses 11% lower
k
cat
d-xylobiose and much lower stabilities to temperature and pH. Here, we performed saturation mutagenesis of W145 and discovered that the
variants express K
i values that are 1.5–2.7-fold (d-glucose) and 1.9–4.6-fold (d-xylose) those of wild-type enzyme. W145F, W145L, and W145Y express good stability and, respectively, 11, 6, and 1% higher
k
cat
d-xylobiose than that of the wild type. At 0.1 M d-xylobiose and 0.1 M d-xylose, kinetic parameters indicate that W145F, W145L, and W145Y catalytic activities are respectively 46, 71, and 48% greater
than that of the wild-type enzyme. 相似文献
18.
Zusammenfassung Das Murein (Peptidoglycan) eines aus Faeces isolierten Streptococcus, der in den wichtigsten Merkmalen mit Peptostreptococcus evolutus (Prevot) Smith übereinstimmt, weist folgende Molverhältnisse auf (aufgerundete bzw. abgerundete Zahlen): Mur:GlcNH2:Ala:Glu:Lys:Gly=1:1:3:1:1:1. Das Verhältnis l-Alanin:d-Alanin=2,15:1. Die Glutaminsäure liegt in der d-Konfiguration und als Amid vor.Durch die Partialhydrolyse der Zellwände und die anschließende Isolierung und Identifizierung der Peptide konnte die Aminosäuresequenz des Mureins geklärt werden. Das Tetrapeptid stimmt mit der üblichen Sequenz l-Ala-d-Glu-NH2-l-Lys-d-Ala der meisten übrigen Bakterien überein. Die Quervernetzung des Mureins wird durch das Peptid Glycyl-l-Alanin hergestellt, wobei l-Alanin an die -Aminogruppe des Lysins gebunden ist. Die Dinitrophenylierung der Zellwand ergab, daß 35% des Glycins und 6% des Lysins eine freie Aminogruppe aufweisen. Die Quervernetzung ist demnach nur zu höchstens 60% durchgeführt.
The chemical composition of the cell walls of Streptococci III. The amino acid sequence of a glycine containing murein from Peptostreptococcus evolutus (Prevot) Smith
Summary Peptostreptococcus evolutus was isolated from feces. Its murein containes muramic acid, glucosamine, alanine, d-glutamic acid, lysine and glycine at a molar ratio of about 1:1:3:1:1:1. The ratio of l-alanine: d-alanine is 2,15:1. Glutamic acid is present as an amide.By acid partial hydrolysis of the cell walls and subsequent isolation and identification of the peptides the amino acid sequence of the murein was elucidated. The tetrapeptide is identical with that of most bacteria (l-Ala-d-Glu-NH2-l-Lys-d-Ala). The crosslinking of the murein is performed by the peptide glycyl-l-alanine. l-alanine is attached to the -amino group of lysine while the amino group of glycine is bound to the carboxyl group of the c-terminal d-alanine of an adjacent tetrapeptide. About 35% glycine and 6% lysine of the murein are dinitrophenylisable indicating that maximally 60% of the possible cross-linkages are realized.相似文献
19.
Saccharomyces cerevisiae is sensitive to d-amino acids: those corresponding to almost all proteinous l-amino acids inhibit the growth of yeast even at low concentrations (e.g. 0.1 mM). We have determined that d-amino acid-N-acetyltransferase (DNT) of the yeast is involved in the detoxification of d-amino acids on the basis of the following findings. When the DNT gene was disrupted, the resulting mutant was far less tolerant
to d-amino acids than the wild type. However, when the gene was overexpressed with a vector plasmid p426Gal1 in the wild type
or the mutant S. cerevisiae as a host, the recombinant yeast, which was found to show more than 100 times higher DNT activity than the wild type, was
much more tolerant to d-amino acids than the wild type. We further confirmed that, upon cultivation with d-phenylalanine, N-acetyl-d-phenylalanine was accumulated in the culture but not in the wild type and hpa3Δ cells overproducing DNT cells. Thus, d-amino acids are toxic to S. cerevisiae but are detoxified with DNT by N-acetylation preceding removal from yeast cells. 相似文献
20.
Abundance of d isomers of amino acids has been used in studies of organic matter diagenesis to determine the contribution of bacterial biomass to the organic matter, especially in marine sediments. However, fluxes of d amino acids in pelagic waters are poorly known. Here we present seasonal changes (March–September) in concentrations of dominant d amino acids in the pool of dissolved free and combined (hydrolysable) amino acids (DFAA and DCAA) in the shallow Roskilde Fjord, Denmark. The amino acid dynamics are related to pelagic bacterial density and activity and abundance of viruses. d␣isomers made up 3.6 and 7.9% of the DFAA and DCAA (average values), respectively, and had similar seasonal variations in concentrations. In batch cultures (0.7- and 0.2-m filtered water in a 1:9 mixture) microbial activity reduced l+d DCAA concentrations in seven of ten sampling dates, while DCAA were released at the remaining three sampling times. NH4+ balance (uptake or release) in the cultures correlated significantly with variations in concentrations of d-DCAA, but not with the total DCAA pools. Abundance of viruses did not correlate with density or production of bacteria in the fjord, but covaried with mineralization of total C, DCAA and PO43− in the batch cultures. The content of d amino acids in bacterial biomass in the cultures varied from 6.7 to 12.5% and correlated with the d isomer concentration in the fjord, except for d-Ala. In an additional six-day batch culture study, DCAA and d-DCAA were assimilated by the bacteria during the initial 36 h, but were released between 36 and 42 h simultaneous with a decline in the bacterial density. Our results demonstrate that peptidoglycan components contribute to natural amino acid pools and are assimilated by bacterial assemblages. This cell wall “cannibalism” ensures an efficient recycling of nutrients within the microbial community. Significant positive correlations between viral abundance and bacterial mineralization of organic matter in the fjord indicated that viral lysis contributed to this nutrient recycling. 相似文献