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1.
    
Summary l-Galactose,d-arabinose, andl-fucose form six-membered rings with identical stereoconfigurations. However, onlyl-fucose can serve as the sole carbon and energy source of wild-typeEscherichia coli K-12. A mutant that can grow onl-galactose andd-arabinose was isolated by alternate selection on the two sugars. Thel-fucose pathway became inducible by all three sugars. Transduction into the mutant of the wild-type fuc+ region containing both the regulatory and structural genes abolished the novel growth abilities onl-galactose andd-arabinose, whereas transduction into the mutant of a fuc deletion abolished the growth abilities on all three sugars. Introduction of the wild-type fucR+ (which encodes the activator protein for the fuc regulon) on a multicopy plasmid depressed the growth abilities of the mutant onl-galactose andd-arabinose, but not onl-fucose. The results suggest that the effector specificity of the activator protein in the mutant was broadened. It is proposed that an adaptive response of an activator-controlled system is more likely than that of a repressor-controlled system to achieve fixation in a population, because the first variant to emerge in response to a novel metabolic demand has a good chance of having an altered specificity of regulation. Such a change entails little or no metabolic liability during the absence of the novel substrate. In contrast, the first variant of a negatively controlled system to emerge has an overwhelming chance of being the result of a random mutation that destroys repressor function. Although negatively controlled systems can be more opportunistic in exploiting new conditions than positively controlled systems, an adaptive change is less likely to become fixed because of the cost associated with gratuitous constitutive gene expression in the absence of the substrate.  相似文献   

2.
    
N-Nitroso-l-arginine was described as one of the products of l-arginine metabolism in biological media. A simple and rapid method to determine its concentration in rat brain was developed. Capillary electrophoresis with a photodiode-array detector was used at 254 nm, permitting the quantification of N-nitroso-l-arginine. The detection limit in biological solution was 1 μg/ml.  相似文献   

3.
    
Summary A polysaccharide producing strain ofBacillus licheniformis was isolated from exudate of raffia palm,Raffia vinifera. The optimum conditions for growth and polysaccharide production have been investigated and established. No appreciable polysaccharide was formed on glucose. It grew best in Czapek-Dox media with sucrose as the carbon source. The polysaccharide has been characterized as a heteropolymer containingd-glucose,d-mannose andd-xylose.  相似文献   

4.
    
Summary Crosslinking of [14C]l-tyrosine to at least five hamster melanoma cell surface proteins is reported. This effect was abolished by addition of nonradioactivel-tyrosine,l-phenylalanine, orl-dopa, but not byd-tyrosine, tyramine, dopamine, norepinephrine, or epinephrine. The above proteins can be purified by tyrosine-affinity chromatography. They have molecular weights different from proteins staining for dopa oxidase and proteins that bind anti-tyrosinase antibody in Western blots. It is suggested that they may be a hithergo unrecognized part of the cellular apparatus governing melanogenesis.  相似文献   

5.
    
Polycationic amino acids induce the leakage and fusion of liposomes containing anionic lipids. We have investigated the nature and extent of the changes in membrane physical properties caused by these polypeptides which could result in the observed membrane destabilization. We found that in the range of pH 5 to pH 7 both poly-l-histidine and poly-l-lysine were ineffective in shifting the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine, either in the presence of absence of 1-palmitoyl-2-oleoylphosphatidylserine. We also studied the gel to liquid crystalline phase transition properties of 11 mixtures of phosphatidylserine and phosphatidylethanolamine, both in dimyristoyl forms as well as the 1-palmitoyl-2-oleoyl forms, as a function of pH and in the presence and absence of polycationic amino acids. We observed that these two lipids were largely miscible at all pH values and in the presence and absence of the polypeptides. However, there was some increased tendency for phase separation at higher pH and in the absence of polypeptide. Thus neither changes in curvature strain nor lateral phase separation induced by the polycationic amino acids could account for their marked ability to induce leakage and fusion.Phosphatidylethanolamine labelled with pyrene on one of the acyl chains gives rise to fluorescent emission from both monomer and excimer forms. The ratio of emission intensity from these two forms is indicative of lateral phase separation and the degree of lateral mobility of this probe. In equimolar mixtures of the 1-palmitoyl-2-oleoyl forms of phosphatidylserine and phosphatidylethanolamine in the liquid crystalline phase at 30 °C we find little effect of pH on the ratio of excimer to monomer emission intensity. However poly-l-lysine markedly lowers the fraction of excimer emission from these liposomes through the pH range from 5 to 7. Poly-l-histidine lowers the excimer to monomer emission ratio at pH 5 but not at pH 7. This is opposite to what one would expect for lateral phase separation and is interpreted at being the consequence of the polypeptide lowering the rate of lateral diffusion of the lipids. This effect of poly-l-histidine is observed over a range of temperatures from 0 to 40°C in both gel and liquid crystalline phases. There is no evidence from the behaviour of the pyrene fluorescent probe for lipid interdigitation. We conclude that the promotion of leakage and fusion in anionic liposomes by polycationic amino acids is not a result of large changes in the physical properties or arrangements of the lipids but rather to a surface binding of the polyamino acids.Abbreviations DSC differential scanning calorimetry - DEPE dielaidoylphosphatidylethanolamine - POPS 1-palmitoyl-2-oleoylphosphatidylethanolamine - DMPS dimyristoylphosphatidylserine - DMPE dimyristoylphosphatidylethanolamine - POPE 1-palmitoyl-2-oleoylphosphatidylethanolamine - TH bilayer to hexagonal phase transition temperature - pyr-PE 1-hexadecanoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphoethanolaline - E/M ratio of intensities of excimer to monomer emission  相似文献   

6.
    
The recombinant Pichia pastoris harboring an improved methionine adenosyltransferase (MAT) shuffled gene was employed to biosynthesize S-adenosyl-l-methionine (SAM). Two l-methionine (l-Met) addition strategies were used to supply the precursor: the batch addition strategy (l-Met was added separately at three time points) and the continuous feeding strategies (l-Met was fed continuously at the rate of 0.1, 0.2, and 0.5 g l−1 h−1, respectively). SAM accumulation, l-Met conversion rate, and SAM productivity with the continuous feeding strategies were all improved over the batch addition strategy, which reached 8.46 ± 0.31 g l−1, 41.7 ± 1.4%, and 0.18 ± 0.01 g l−1 h−1 with the best continuous feeding strategy (0.2 g l−1 h−1), respectively. The bottleneck for SAM production with the low l-Met feeding rate (0.1 g L−1 h−1) was the insufficient l-Met supply. The analysis of the key enzyme activities indicated that the tricarboxylic acid cycle and glycolytic pathway were reduced with the increasing l-Met feeding rate, which decreased the adenosine triphosphate (ATP) synthesis. The MAT activity also decreased as the l-Met feeding rate rose. The reduced ATP synthesis and MAT activity were probably the reason for the low SAM accumulation when the l-Met feeding rate reached 0.5 g l−1 h−1.  相似文献   

7.
    
Employing a photoaffinity labeling procedure with 8-azido-S-adenosyl-l-[methyl-3H]methionine (8-N3-Ado[methyl-3H]Met), the binding sites for S-adenosyl-l-methionine (AdoMet) of three protein N-methyltransferases [AdoMet:myelin basic protein-arginine N-methyltransferase (EC2.1.1.23); AdoMet:histone-arginin N-methyltransferase (EC2.1.1.23); and AdoMet:cytochromec-lysine N-methyltransferase (EC2.1.1.59)] have been investigated. The incorporation of the photoaffinity label into the enzymes upon UV irradiation was highly specific. In order to define the AdoMet binding sites, the photolabeled enzymes were sequentially digested with trypsin, chymotrypsin, and endoproteinase Glu-C. After each proteolytic digestion, radiolabeled peptide from each enzyme was resolved on HPLC first by gradient elution and further purified by an isocratic elution. Retention times of the purified radiolabeled peptides from the three enzymes from the corresponding proteolysis were significantly different, indicating that their sizes and compositions were different. Amino acid composition analysis of these peptides confirmed further that the AdoMet binding sites of these protein N-methyltransferases are quite different.  相似文献   

8.
    
A liquid chromatographic method has been developed for the determination of 3-nitro-l-tyrosine. Different detection methods, including UV, oxidative and redox electrochemistry, and postcolumn photolysis followed by electrochemical detection, have been optimized and compared in terms of analysis time, detection limit and dynamic range. It was demonstrated that liquid chromatography with postcolumn photolysis followed by electrochemical detection is the most effective method, with an analysis time of 5 min, detection limit of 0.01 pmol, and a linear dynamic range from 2 nM to 100 μM.  相似文献   

9.
    
A simple, general scheme for the synthesis of sulfhydryl-specific alkyl alkanethiolsulfonate (RSSO2R) reagents where R is methyl, has been developed. Two new reagents, methyl aminoethanethiolsulfonate (2) and methyl benzylthiolsulfonate (3) were synthesized. These were used to modify stoichiometrically and selectively under mild conditions the sulfhydryl groups ofN-acetyl-l-cysteine ethyl ester (4),N-acetyl-l-cysteinep-nitroanilide (7), glutathione, and the A chain of bovine insulin. The corresponding -S-(-aminoethanethiol) and -S-(benzylthiol) derivatives ofl-cysteine and of the peptides were afforded. The characteristics and significance of these reactions and products are discussed.  相似文献   

10.
  总被引：1，自引：0，他引：1  
The effects of nitrogen limitation and recovery on nitrogen-containing macromolecules were followed in the cyanobacterium Aphanocapsa 6308. Removal of nitrogen from growth media triggers the degradation of the endogenous nitrogen reserves phycocyanin and cyanophycin granule polypeptide in the cyanobacterium Aphanocapsa 6308. Nitrogen recovery involves immediate synthesis of cyanophycin granule polypeptide with peak levels of 5–12% of cell dry weight found 8–12 h after a utilizable nitrogen source is added. A rapid decrease in cyanophycin granule polypeptide level then occurs and the level remains low even in light-limited stationary growth with all nitrogen sources tested except nitrate and ammonia. Protein and phycocyanin recoveries began 3 h after a utilizable nitrogen source was added. Data suggest continuous activity of the enzyme system synthesizing cyanophycin granule polypeptide in nitrogen-limited cells, but synthesis of a degrading system only after nitrogen recovery begins.Nonstandard Abbreviations CGP Cyanophycin granule polypeptide - CAP chloramphenicol - PC phycocyaninTo whom offprint requests should be sent  相似文献   

11.
Summary Proline and Pro-derived peptidomimetics, such as meoxPro-Oic (4-methoxy-proline-octahydro indolic acid), and DBF (2-aminoethyl-6-dibenzofuran propionic acid) were introduced into thymopentin-derived penta-[SP5-] and hexa-[SP6-] peptides and penta-, hexa- and hepta-alanine. Surprisingly, we found that cyclomonomer formation in the investigated penta- and hexapeptides was drastically hindered by the presence of proline regardless of position.  相似文献   

12.
    
Seedlings of red radish (Raphanus sativus L. var. sativus) accumulated high amounts of free malic acid and sinapoylmalate, when grown on nitrate as the sole N-source. In the presence of ammonium (NO3–: NH4+, 1:2) both metabolites failed to accumulate, and the levels of arginine, asparagine, glutamine, histidine, and serine were greatly increased. The extractable activity of 1-sinapoylglucose: l-malate sinapoyltransferase, an enzyme which plays a key role in channelling malic acid into the sinapic-acid metabolism of this plant, was positively correlated with the malic-acid level in cotyledons. The possibility is discussed that free malic acid might be the likely candidate for regulating the activity of 1-sinapoylglucose: l-malate sinapoyltransferase.Abbreviation SMT sinapoylglucose: L-malate sinapoyltransferase  相似文献   

13.
A significant improvement in the production of l-ribulose from inexpensive and commercially available starting materials, l-arabinose and sodium aluminate, is demonstrated. This has facilitated expeditious access to gram-scale quantities of l-ribulofuranoside derivatives.  相似文献   

14.
N-Acetyl-L-glutamate (NAG), the activator of mitochondrial carbamoyl phosphate synthetase (CPS), is demonstrated by several methods, including a new HPLC assay, in the brain of mammals and of chicken. The brain levels of NAG are 200–300 times lower than the levels of N-acetyl-l-aspartate (NAA), and are similar to the levels of NAG in rat liver. The NAG levels in chicken liver are very low. Although NAG is mitochondrial in the liver, it is cytosolic in brain. Using enzyme activity and immuno assays we did not detect CPS in brain (detection limit, 12.5 g/g brain), excluding that brain NAG is involved in citrullinogenesis. The regional distribution of brain NAG differs from that of NAA and resembles that of N-acetyl-l-aspartyl-l-glutamate (NAAG), suggesting that NAG and NAAG are related. NAG might be involved in the modulation of NAAG degradation.Special issue dedicated to Dr. Santiago Grisolía  相似文献   

15.
    
Cell-free extracts of d-fructose grown cells of Pseudomonas putida, P. fluorescens, P. aeruginosa, P. stutzeri, P. mendocina, P. acidovorans and P. maltophila catalyzed a P-enolpyruvate-dependent phosphorylation of d-fructose and contained 1-P-fructokinase activity suggesting that in these species fructuse-1-P and fructose-1,6-P2 were intermediates of d-fructose catabolism. Neither the 1-P-fructokinase nor the activity catalyzing a P-enolpyruvate-dependent phosphorylation of d-fructose was present in significant amounts in succinate-grown cells indicating that both activities were inducible. Cell-free extracts also contained activities of fructose-1,6-P2 aldolase, fructose-1,6-P2 phosphatase, and P-hexose isomerase which could convert fructose-1,6-P2 to intermediates of either the Embden-Meyerhof pathway or Entner-Doudoroff pathway. Radiolabeling experiments with 1-14C-d-fructose suggested that in P. putida, P. aeruginosa, P. stutzeri, and P. acidovorans most of the alanine was made via the Entner-Doudoroff pathway with a minor portion being made via the Embden-meyerhof pathway. An edd- mutant of P. putida which lacked a functional Entner-Doudoroff pathway but was able to grow on d-fructose appeared to make alanine solely via the Embden-Meyerhof pathway.Non-Standard Abbreviations cpm counts per min - edd- mutant lacking Entner-Doudoroff dehydrase (6-PGA dehydrase) - EDP Entner-Doudoroff pathway - EMP Embden-Meyerhof pathway - FDP fructose-1,6-P2 - FDPase FDP phosphatase - F-1-P fructose-1-P - F-6-P fructose-6-P - FPTs PEP: d-fructose phosphotransferase system - G-6-P glucose-6-P - KDPG 2-keto-3-deoxy-6-P-gluconate - PEP P-enolpyruvate - 1-PFK 1-P-fructokinase - 6-PFK 6-P-fructokinase - 6-PGA 6-P-gluconate  相似文献   

16.
    
1. One binding component with aKd value of 200×10–9 M and half-life of the ligand binding component of 30 min was found. 2. Chloride ions produced a significant increase ofl-[3H]aspartate andl-[3H]glutamate binding. 3.l-Glutamate,l-ibotenate,l-quisqualate, anddl-homocysteic acid were potent inhibitors ofl-[3H]aspartate binding. 4. In all brain regions major increases of binding were observed during the third week of the in ovo period of life.  相似文献   

17.
    
Nocardia sp. 239 is able to use l-tyrosine and both d- and l-phenylalanine as carbon-, energy- and nitrogen sources for growth. The catabolism of these compounds is by way of (4-hydroxy)phenylpyruvate and (4-hydroxy)-phenylacetate as intermediates and the pathways merge at the level of homogentisate. The conversion of the amino acids into (4-hydroxy)phenylpyruvate is catalyzed by an inducible NAD-dependent phenylalanine dehydrogenase and l-tyrosine aminotransferase, respectively. Incubation of the organism in media with l-phenylalanine plus phenyl-pyruvate resulted in diauxic growth, with phenylpyruvate used first. Phenylalanine dehydrogenase activity cold only be detected after depletion of phenylpyruvate, in the ensuing second growth phase on l-phenylalanine. During growth on phenylalanine plus methanol, low levels of phenylalanine dehydrogenase were detected and this resulted in simultaneous utilization of the two substrates. Following diepoxyoctane treatment, mutants of Nocardia sp. 239 affected in phenylalanine and phenylpyruvate degradation were isolated. Double mutants blocked in both phenylalanine dehydrogenase and phenylpyruvate decarboxylase completely failed to catabolize phenylalanine. The absence of these enzymes did not affect growth on tyrosine.Abbreviations RuMP ribulose monophosphate - EMS ethylmethanesulphonate - NTG N-methyl-N-nitro-N-nitrosoguanidine  相似文献   

18.
Yeom SJ  Ji JH  Yoon RY  Oh DK 《Biotechnology letters》2008,30(10):1789-1793
Geobacillus thermodenitrificans, with a double-site mutation in L: -arabinose isomerase, produced 95 g L-: ribulose l(-1 ) from 500 g L: -arabinose l(-1) under optimum conditions of pH 8, 70 degrees C, and 10 units enzyme ml(-1) with a conversion yield of 19% over 2 h. The half-lives of the mutated enzyme at 70 and 75 degrees C were 35 and 4.5 h, respectively.  相似文献   

19.
The catabolism of d-galactose in yeast depends on the enzymes of the Leloir pathway. In contrast, Aspergillus nidulans mutants in galactokinase (galE) can still grow on d-galactose in the presence of ammonium—but not nitrate—ions as nitrogen source. A. nidulans galE mutants transiently accumulate high (400 mM) intracellular concentrations of galactitol, indicating that the alternative d-galactose degrading pathway may proceed via this intermediate. The enzyme degrading galactitol was identified as l-arabitol dehydrogenase, because an A. nidulans loss-of-function mutant in this enzyme (araA1) did not show NAD+-dependent galactitol dehydrogenase activity, still accumulated galactitol but was unable to catabolize it thereafter, and a double galE/araA1 mutant was unable to grow on d-galactose or galactitol. The product of galactitol oxidation was identified as l-sorbose, which is a substrate for hexokinase, as evidenced by a loss of l-sorbose phosphorylating activity in an A. nidulans hexokinase (frA1) mutant. l-Sorbose catabolism involves a hexokinase step, indicated by the inability of the frA1 mutant to grow on galactitol or l-sorbose, and by the fact that a galE/frA1 double mutant of A. nidulans was unable to grow on d-galactose. The results therefore provide evidence for an alternative pathway of d-galactose catabolism in A. nidulans that involves reduction of the d-galactose to galactitol and NAD+-dependent oxidation of galactitol by l-arabitol dehydrogenase to l-sorbose.  相似文献   

20.
    
The induction of extracellular arabinases by pentose sugars and polyols generated by the metabolic pathway of l-arabinose and d-xylose catabolism in Aspergillus niger was investigated. Induction occurred with l-arabinose and l-arabitol but not with d-xylose or xylitol. l-arabitol in particular was found to be a good inducer for -l-arabinofuranosidase and endo-arabinase activities. Western blotting analysis showed both -l-arabinofuranosidase A and B to be present. No induction was observed using d-arabitol. Unlike the wild type A. niger N402 strain, the A. niger xylulose kinase negative mutant N572 also showed induction of -l-arabinofuranosidases A and B and endo-arabinase activity on d-xylose and xylitol. This is due to metabolic conversion of these compounds leading to the accumulation of both xylitol and l-arabitol in this mutant, the latter of which then acts as inducer. The induction of the two -l-arabinofuranosidases and endo-arabinase is under the control of two regulatory systems namely pathway specific induction and carbon catabolite repression. Under derepressing conditions in the wild type only -l-arabinofuranosidase B could be detected by Western blotting analysis. This indicates that -l-arabinofuranosidase B is of importance in the initiation of specific induction of the various arabinose activities in A. niger grown on arabinose containing structural polysaccharides.Abbreviations PNA p-nitrophenyl--l-arabinofuranoside  相似文献   

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