共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary Two classes of partial revertants of 00-type mutants in the pyruvate dehydrogenase system ofEscherichia coli K 12 could be distinguished enzymatically and genetically. In one class of these strains the second mutation has occurred at or near the primary 00 site. The partial revertants of this class synthesize a pyruvate dehydrogenase complex containing a defective carboxylase component. The strains of the other class proved to be suppressed 00-type mutants,the second mutation having occurred outside the acetate locus on the E. coli chromosome. One of the suppressor alleles was found to be specific for a certain 00 site; it did not act on another genetically distinguishable 00 site nor on any of the tested mutant sites in the pyruvate dehydrogenase genes. The suppressed 00 type strains synthesize only small amounts (about 1/50 of wild type) of pyruvate dehydrogenase with a carboxylase component which so far could not be distinguished from the wild type carboxylase. In addition, the suppressor gene mutants produce a partial complex of the pyruvate dehydrogenase which lacks the carboxylase component. It is not yet known whether or not this situation represents a disproportional synthesis of the constituent enzymes of the pyruvate dehydrogenase complex, i.e., production of smaller amounts of the carboxylase than required for the formation of the enzyme complex.The results are discussed regarding their significance for the regulation of protein biosynthesis inE. coli in connection with similar data of other authors (Jacob andMonod 1961;Beckwith 1963, 1964) obtained with the lactose system of the same organism.
Mit 2 Textabbldungen 相似文献
Mit 2 Textabbldungen 相似文献
2.
The effect of different amounts of supplemented l-isoleucine and pantothenate has been analysed with the auxotrophic strain Corynebacterium glutamicum
ΔilvA
ΔpanB, showing that the final biomass concentration of this preliminary l-valine production strain can be controlled by the amount of added l-isoleucine. One gramme cell dry weight is formed from 48 μmol l-isoleucine. Different amounts of available pantothenate affect the intracellular pyruvate concentration. By limiting pantothenate
supplementation from 0.8 to 0.1 μM, a 35-fold increase of cytoplasmic pyruvate up to 14.2 mM can be observed, resulting in
the increased formation of l-valine, l-alanine and organic acids in the presence of low pantothenate concentrations. These findings can be used to redirect the
carbon flux from glycolysis via pyruvate to the TCA cycle towards the desired product l-valine. 相似文献
3.
Raymond Mengual Marie-Hélène Claude-Schlageter Jean-Claude Poiree Micael Yagello Pierre Sudaka 《The Journal of membrane biology》1989,108(3):197-205
Summary The experiments reported in this paper aim at characterizing the carboxylic acid transport, the interactions of pyruvate and citrate with their transport sites and specificity. The study of these carriers was performed using isotopic solutes for the influx measurements in brush-border membrane vesicles under zerotrans conditions where the membrane potential was abolished with KCl preloading with valinomycin or equilibrium exchange conditions and =0.Under zerotrans condition and =0, the influence of pyruvate concentrations on its initial rates of transport revealed the existence of two families of pyruvate transport sites, one with a high affinity for pyruvate (K
t
=88 m) and a low affinity for sodium (K
t
=57.7mm) (site I), the second one with a low affinity for pyruvate (K
t
=6.1mm) and a high affinity for sodium (K
t
=23.9mm) (site II). The coupling factor [Na]/[pyruvate] stoichiometry were determined at 0.25mm and 8mm pyruvate and estimated at 1.8 for site I, and 3 when the first and the second sites transport simultaneously.Under chemical equilibrium (0) single isotopic labeling, transport kinetics of pyruvate carrier systems have shown a double interaction of pyruvate with the transporter; the sodium/pyruvate stoichiometry also expressed according to a Hill plot representation wasn=1.7. The direct method of measuring Na+/pyruvate stoichiometry from double labeling kinetics and isotopic exchange, for a time course, gives an=1.67.Studies of transport specificity, indicate that the absence of inhibition of lactate transport by citrate and the existence of competitive inhibition of lactate and citrate transports by pyruvate leads to the conclusion that the low pyruvate affinity site can be attributed to the citrate carrier (tricarboxylate) and the high pyruvate affinity site to the lactate carrier (monocarboxylate). 相似文献
4.
Zhu L Tao R Wang Y Jiang Y Lin X Yang Y Zheng H Jiang W Yang S 《Applied microbiology and biotechnology》2011,90(3):903-910
l-2-Aminobutyric acid can be synthesized in a transamination reaction from l-threonine and l-aspartic acid as substrates by the action of threonine deaminase and aromatic aminotransferase, but the by-product l-alanine was produced simultaneously. A small amount of l-alanine increased the complexity of the l-2-aminobutyric acid recovery process because of their extreme similarity in physical and chemical properties. Acetolactate
synthase has been introduced to remove the pyruvate intermediate for reducing the l-alanine concentration partially. To eliminate the remnant l-alanine, alanine racemase of Bacillus subtilis in combination with d-amino acid oxidase of Rhodotorula gracilis or Trigonopsis variabilis respectively was introduced into the reaction system for the l-2-aminobutyric acid synthesis. l-Alanine could be completely removed by the action of alanine racemase of B. subtilis and d-amino acid oxidase of R. gracilis; thereby, high-purity l-2-aminobutyric acid was achieved. The results revealed that alanine racemase could discriminate effectively between l-alanine and l-2-aminobutyric acid, and selectively catalyzed l-alanine to d-alanine reversibly. d-Amino acid oxidase then catalyzed d-alanine to pyruvate stereoselectively. Furthermore, this method was also successfully used to remove the by-product l-alanine in the production of other neutral amino acids such as l-tertiary leucine and l-valine, suggesting that multienzymatic whole-cell catalysis can be employed to provide high purity products. 相似文献
5.
Blombach B Schreiner ME Moch M Oldiges M Eikmanns BJ 《Applied microbiology and biotechnology》2007,76(3):615-623
Intracellular precursor supply is a critical factor for amino acid productivity of Corynebacterium glutamicum. To test for the effect of improved pyruvate availability on l-lysine production, we deleted the aceE gene encoding the E1p enzyme of the pyruvate dehydrogenase complex (PDHC) in the l-lysine-producer C. glutamicum DM1729 and characterised the resulting strain DM1729-BB1 for growth and l-lysine production. Compared to the host strain, C. glutamicum DM1729-BB1 showed no PDHC activity, was acetate auxotrophic and, after complete consumption of the available carbon sources
glucose and acetate, showed a more than 50% lower substrate-specific biomass yield (0.14 vs 0.33 mol C/mol C), an about fourfold
higher biomass-specific l-lysine yield (5.27 vs 1.23 mmol/g cell dry weight) and a more than 40% higher substrate-specific l-lysine yield (0.13 vs 0.09 mol C/mol C). Overexpression of the pyruvate carboxylase or diaminopimelate dehydrogenase genes
in C. glutamicum DM1729-BB1 resulted in a further increase in the biomass-specific l-lysine yield by 6 and 56%, respectively. In addition to l-lysine, significant amounts of pyruvate, l-alanine and l-valine were produced by C. glutamicum DM1729-BB1 and its derivatives, suggesting a surplus of precursor availability and a further potential to improve l-lysine production by engineering the l-lysine biosynthetic pathway.
This study is dedicated to Prof. Dr. Hermann Sahm on the occasion of his 65th birthday. 相似文献
6.
Summary A defective phage 80.1 was obtained which carries anamber suppressor locus (su
y
, most likely identical tosu
III
ofBrenner andBeckwith, 1965) and part of the tryptophan operon fromE. coli K 12. Various homo- and heterogenotes with respect to this suppressor locus have been isolated. The action of theamber suppressor locus onamber sites in the decarboxylase gene of the pyruvate dehydrogenase complex and onT 4 amber mutants was tested. In all cases the suppressor in its active state (su
y
+; i. e., suppressingamber sites) was dominant over the suppressor in the inactive (su
y
–) state. The presence of anotheramber suppressor (su
II
) in the host did not alter the expression ofsu
y
towardsT 4 amber mutants. Further evidence was obtained for the specificity of theamber suppression. While remaining unsuppressed in strains harboringsu
II
, twoamber sites of the O0-type in one of the pyruvate dehydrogenase genes are suppressed bysu
y
in heterogenotessu
II
+/su
y
+.The kinetics of the expression of the suppressor locus after infection with the defective 80.1 carryingsu
y
+ was tested and compared for the production of pyruvate dehydrogenase andT 4 amber mutants. Comparable rates of suppressed synthesis of the enzyme appeared to be reached much later than the formation ofT 4 amber mutants.Herrn ProfessorGeorg Melchers zum 60. Geburtstag gewidmet. 相似文献
7.
Kenro Tokuhiro Nobuhiro Ishida Eiji Nagamori Satoshi Saitoh Toru Onishi Akihiko Kondo Haruo Takahashi 《Applied microbiology and biotechnology》2009,82(5):883-890
Expression of a heterologous l-lactate dehydrogenase (l-ldh) gene enables production of optically pure l-lactate by yeast Saccharomyces cerevisiae. However, the lactate yields with engineered yeasts are lower than those in the case of lactic acid bacteria because there
is a strong tendency for ethanol to be competitively produced from pyruvate. To decrease the ethanol production and increase
the lactate yield, inactivation of the genes that are involved in ethanol production from pyruvate is necessary. We conducted
double disruption of the pyruvate decarboxylase 1 (PDC1) and alcohol dehydrogenase 1 (ADH1) genes in a S. cerevisiae strain by replacing them with the bovine l-ldh gene. The lactate yield was increased in the pdc1/adh1 double mutant compared with that in the single pdc1 mutant. The specific growth rate of the double mutant was decreased on glucose but not affected on ethanol or acetate compared
with in the control strain. The aeration rate had a strong influence on the production rate and yield of lactate in this strain.
The highest lactate yield of 0.75 g lactate produced per gram of glucose consumed was achieved at a lower aeration rate. 相似文献
8.
In Saccharomyces cerevisiae the utilization of lactate occurs via specific oxidation of l- and d-lactate to pyruvate catalysed by l-lactate ferricytochrome c oxidoreductase (L-LCR) (EC 1.1.2.3) encoded by the CYB2 gene, and d-lactate ferricytochrome c oxidoreductase (D-LCR) (EC 1.1.2.4), respectively. We selected several lactate– pyruvate+ mutants in a cyb2 genetic background. Two of them were devoid of D -LCR activity (dld mutants, belonging to the same complementation group). The mutation mapped in the structural gene. This was demonstrated by a gene dosage effect and by the thermosensitivity of the enzyme activity of thermosensitive revertants. The DLD gene was cloned by complementation for growth on d-, l-lactate in the strain WWF18-3D, carrying both a CYB2 disruption and the dld mutation. The minimal complete complementing sequence was localized by subcloning experiments. From the sequence analysis an open reading frame (ORF) was identified that could encode a polypeptide of 576 amino-acids, corresponding to a calculated molecular weight of 64000 Da. The deduced protein sequence showed significant homology with the previously described microsomal flavoprotein l-gulono--lactone oxidase isolated from Rattus norvegicus, which catalyses the terminal step of l-ascorbic acid biosynthesis. These results are discussed together with the role of L-LCR and D-LCR in lactate metabolism of S. cerevisiae. 相似文献
9.
K. Sonntag J. Schwinde A. A. de Graaf A. Marx B. J. Eikmanns W. Wiechert H. Sahm 《Applied microbiology and biotechnology》1995,44(3-4):489-495
The carbon flux distribution in the central metabolism of Corynebacterium glutamicum was studied in batch cultures using [1-13C]- and [6-13C]glucose as substrate during exponential growth as well as during overproduction of l-lysine and l-glutamate. Using the 13C NMR data in conjunction with stoichiometric metabolite balances, molar fluxes were quantified and normalised to the glucose uptake rate, which was set to 100. The normalised molar flux via the hexose monophosphate pathway was 40 during exponential growth, whereas it was only 17 during l-glutamate production. During l-lysine production, the normalised hexose monophosphate pathway flux was elevated to 47. Thus, the carbon flux via this pathway correlated with the NADPH demand for bacterial growth and l-lysine overproduction. The normalised molar flux in the tricarboxylic acid cycle at the level of 2-oxoglutarate dehydrogenase was 100 during exponential growth and 103 during l-lysine secretion. During l-glutamate formation, the normalised flux through the tricarboxylic acid cycle was reduced to 60. In contrast to earlier NMR studies with C. glutamicum, no significant activity of the glyoxylate pathway could be detected. All experiments indicated a strong in vivo flux from oxaloacetate back to phosphoenolpyruvate and/or pyruvate, which might be due to phosphoenolpyruvate carboxykinase activity in C. glutamicum. 相似文献
10.
11.
Summary A method for the positive selection of dadA mutants defective in Dolor-amino acid dehydrogenase has been devised. It consists in isolating mutants resistant to -chroro-Dolor-alanine and screening for mutant colony color on a special agar medium. All 70 Escherichia coli K12 dadA mutants isolated either by this method or by other selection procedures map at a locus which is near to hemA and closely linked with dadR. Since some of the dadA mutants are thermosensitive in Dolor-methionine utilization in vivo and have thermolabile Dolor-amino acid dehydrogenase in vitro, it is proposed that the dadA gene codes for the enzyme structure. The broad substrate specificity, apparent membrane localization, inducibility by alanine, and repressibility by glucose strongly suggest that the Dolor-amino acid dehydrogenase coded by the dadA gene is a species variant of the enzyme described under the same name in Salmonella typhimurium. It may be identical or homologous with the enzymes described under the names alaninase, Dolor-alanine oxidase or Dolor-alanine dehydrogenase in E. coli K12 or B. 相似文献
12.
Regulation of pteridine biosynthesis and aromatic amino acid hydroxylation inDrosophila melanogaster
The relationship between high dietary levels of aromatic amino acid and regulation of pteridines inDrosophila eyes was examined by measuring changes in pool levels of six pterins in the wild type and mutants and amino acid pool levels in flies that carry mutations for pteridine biosynthesis. The effect upon relative viability and developmental times was also analyzed; relative viability was affected byl-phenylalanine,l-tryptophan, andl-tyrosine in decreasing order and thed-amino acids had little or no effect. The changes in concentration of biopterin, dihydrobiopterin, pterin, sepiapterin, drosopterins, and isoxanthopterin showed a characteristic pattern of increased and/or decreased amounts in response to each of the threel-amino acids. Pterin was regularly increased, and isoxanthopterin decreased.l-Tyrosine caused a 2.1-fold increase in dihydrobiopterin, the largest increase found in this study;l-tryptophan also caused dihydrobiopterin to increase butl-phenylalanine did not. Of 18 eye-color mutants examined, 2 were found to contain high levels of phenylalanine and/or tyrosine,Pu
2 andHn
r3. These two mutants, along withpr
c4
cn/pr
m2b
cn, were shown to be very sensitive to dietaryl-phenylalanine, indicating that having low levels of certain pteridines makes them susceptible to toxic effects of these amino acids. Therefore, high levels of aromatic amino acids can perturb the balance among pteridine pools, and low levels of some pteridines in mutants are correlated with the inability to withstand the toxic effects of phenylalanine. From the patterns of change in the pteridines we suggest that tetrahydropterin may also be a cofactor for hydroxylation of phenylalanine, along with tetrahydrobiopterin.This work was sponsored in part by a grant from the U.S.-Spain Joint Committee for Scientific and Technological Cooperation. 相似文献
13.
The effect of gene knockout on metabolism in the pflA–, pflB–, pflC–, and pflD– mutants of Escherichia coli was investigated. Batch cultivations of the pfl
– mutants and their parent strain were conducted using glucose as a carbon source. It was found that pflA– and pflB– mutants, but not pflC– and pflD– mutants, produced large amounts of d-lactate from glucose under the microaerobic condition, and the maximum yield was 73%. In order to investigate the metabolic regulation mechanism, we measured enzyme activities for the following eight enzymes: glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), pyruvate kinase, lactate dehydrogenase (LDH), phosphoenolpyruvate carboxylase, acetate kinase, and alcohol dehydrogenase. Intracellular metabolite concentrations of glucose 6-phosphate, fructose 1,6-bisphosphate, phosphoenolpyruvate, pyruvate, acetyl coenzyme A as well as ATP, ADP, AMP, NADH, and NAD+ were also measured. It was shown that the GAPDH and LDH activities were considerably higher in pflA– and pflB– mutants, which implies coupling between NADH production and consumption between the two corresponding reactions. The urgent energy requirement was shown by the lower ATP/AMP level due to both oxygen limitation and pfl gene knockout, which promoted significant stepping-up of glycolysis when using glucose as a carbon source. It was shown that the demand for energy is more important than intracellular redox balance, thus excess NADH produced through GAPDH resulted in a significantly higher intracellular NADH/NAD+ ratio in pfl
– mutants. Consequently, the homolactate production was achieved to meet the requirements of the redox balance and the energy production through glycolysis. The effect of using different carbon sources such as gluconate, pyruvate, fructose, and glycerol was investigated. 相似文献
14.
Engineering <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis> for the production of pyruvate 总被引:1,自引:0,他引:1
A Corynebacterium glutamicum strain with inactivated pyruvate dehydrogenase complex and a deletion of the gene encoding the pyruvate:quinone oxidoreductase
produces about 19 mM l-valine, 28 mM l-alanine and about 55 mM pyruvate from 150 mM glucose. Based on this double mutant C. glutamicum △aceE △pqo, we engineered C. glutamicum for efficient production of pyruvate from glucose by additional deletion of the ldhA gene encoding NAD+-dependent l-lactate dehydrogenase (LdhA) and introduction of a attenuated variant of the acetohydroxyacid synthase (△C–T IlvN). The latter
modification abolished overflow metabolism towards l-valine and shifted the product spectrum to pyruvate production. In shake flasks, the resulting strain C. glutamicum △aceE △pqo △ldhA △C–T ilvN produced about 190 mM pyruvate with a Y
P/S of 1.36 mol per mol of glucose; however, it still secreted significant amounts of l-alanine. Additional deletion of genes encoding the transaminases AlaT and AvtA reduced l-alanine formation by about 50%. In fed-batch fermentations at high cell densities with adjusted oxygen supply during growth
and production (0–5% dissolved oxygen), the newly constructed strain C. glutamicum △aceE △pqo △ldhA △C–T ilvN △alaT △avtA produced more than 500 mM pyruvate with a maximum yield of 0.97 mol per mole of glucose and a productivity of 0.92 mmol g(CDW)−1 h−1 (i.e., 0.08 g g(CDW)
−1 h−1) in the production phase. 相似文献
15.
Corinne Vander Wauven Alfred Jann Dieter Haas Thomas Leisinger Victor Stalon 《Archives of microbiology》1988,150(4):400-404
Most Pseudomonas aeruginosa PAO mutants which were unable to utilize l-arginine as the sole carbon and nitrogen source (aru mutants) under aerobic conditions were also affected in l-ornithine utilization. These aru mutants were impaired in one or several enzymes involved in the conversion of N2-succinylornithine to glutamate and succinate, indicating that the latter steps of the arginine succinyltransferase pathway can be used for ornithine catabolism. Addition of aminooxyacetate, an inhibitor of the N2-succinylornithine 5-aminotransferase, to resting cells of P. aeruginosa in ornithine medium led to the accumulation of N2-succinylornithine. In crude extracts of P. aeruginosa an ornithine succinyltransferase (l-ornithine:succinyl-CoA N2-succinyltransferase) activity could be detected. An aru mutant having reduced arginine succinyltransferase activity also had correspondingly low levels of ornithine succinyltransferase. Thus, in P. aeruginosa, these two activities might be due to the same enzyme, which initiates aerobic arginine and ornithine catabolism.Abbreviations OAT
ornithine 5-aminotransferase
- SOAT
N2-succinylornithine 5-aminotransferase
- Oru
ornithine utilization
- Aru
arginine utilization 相似文献
16.
E. L. Russell K. B. Storey 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1995,165(2):132-142
The effects of anoxia (N2 atmosphere at 5 °C) or freezing (at-8 °C) exposure in vivo on the activities of five enzymes of carbohydrate metabolism were assessed in foot muscle and hepatopancreases of the marine periwinkle Littorina littorea. Changes in glycogen phosphorylase, glycogen synthetase, pyruvate kinase and pyruvate dehydrogenase under either stress were generally consistent with covalent modification of the enzymes to decrease enzyme activity and/or convert the enzyme to a less active form. However, no evidence for a similar covalent modification of phosphofructokinase was found. The metabolic effects of freezing and anoxia were generally similar, suggesting that a primary contributor to freezing survival is the implementation of anaerobic metabolism and metabolic arrest mechanisms that also promote anoxia survival in marine molluses. However, in hepatopancreas phosphorylase was activated and pyruvate kinase remained in two enzyme forms in freezing-exposed snails, contrary to the results for anoxic animals. Ion exchange chromatography on DE-52 Sephadex revealed the presence of two forms of pyruvate kinase in both tissues of control L. littorea, eluting at 30–50 mmol·1-1 KCl (peak I) or 90–110 mmol·1-1 KCl (peak II). Anoxia exposure converted pyruvate kinase in both tissues to the peak I form, as did freezing for foot muscle pyruvate kinase. Kinetic analysis showed that peak I pyruvate kinase had lower affinities for substrates, phosphoenolpyruvate and ADP, and was very strongly inhibited by l-alanine compared with the peak II enzyme. Peak I pyruvate kinase had an I
50 value for l-alanine of 0.38 mmol·1-1, whereas peak II pyruvate kinase was unaffected by l-alanine evenat 40 mmol·1-1. In vitro incubation of extracts from control foot muscle under conditions promoting phosphorylation or dephosphorylation identified the peak I and II forms as the low and high phosphate forms, respectively. This result for L. littorea pyruvate kinase was highly unusual and contrary to the typical effect of anoxia on pyruvate kinase in marine molluscs which is to stimulate the phosphorylation of pyruvate kinase and, thereby, convert the enzyme to a less active form.Abbreviations
AABS
p-(p-aminophenylazo)benzene sulphonic acid
-
F2, 6P
fructose-2,6-bisphosphate
-
F6P
fructose-6-phosphate
-
G6P
glucose-6-phosphate
-
GP
glycogen phosphorylase
-
GS
glycogen synthase
-
I
50
inhibitor concentration reducing enzyme velocity by 50%
-
MR
metabolic rate
-
PDH
pyruvate dehydrogenase
-
PEP
phosphoenopyruvate
-
PFK
phosphofructokinase
-
PK
pyruvate kinase
-
SW
sea water
-
F
a
air temperature
-
TCA
trichloroacetic acid
-
UDPG
uridine-diphosphate glucose
-
WW
wet weight 相似文献
17.
Summary Two mutants of Saccharomyces cerevisiae lacking pyruvate kinase (EC.2.7.1.40) are described. The mutations are recessive, segregate 2+:2- in tetrads and do not complement each other. Single-step spontaneous revertants, isolated on glucose plates, get back pyruvate kinase activity. The enzymes from various revertants display a wide spectrum of specific activity, thermolability and altered affinity for ligands such as P-enol pyruvate, ADP and fructose 1,6-diphosphate. The mutants produce materials crossreacting to the rabbit antibody raised against purified pyruvate kinase from the wild type yeast. These mutations thus define the structural gene of pyruvate kinase.The mutations map on the leaft arm of chromosome I and form a single complementation group with five other pyruvate kinase mutations in the pyk1 gene that was earlier suggested to be a regulatory locus controlling the synthesis of this enzyme. A comparative study of these mutants has been made with the structural mutants described here. 相似文献
18.
Iris Eggeling Christiana Cordes Lothar Eggeling Hermann Sahm 《Applied microbiology and biotechnology》1987,25(4):346-351
Summary
Corynebacterium glutamicum ATCC 13 032 produces 13 g/l l-isoleucine from 200 mM -ketobutyrate as a synthetic precursor. In fed batch cultures up to 19 g/l l-isoleucine is formed. For optimal conversion the addition of 0.3 mM l-valine plus 0.3 mM l-leucine to the fermentation medium is required. The affinity constants for the acetohydroxy acid synthase (AHAS) were determined. (This enzyme directs the flow of -ketobutyrate plus pyruvate towards l-isoleucine and that of two moles of pyruvate to l-valine and l-leucine, respectively.) For -ketobutyrate the K
m is 4.8×10-3 M, and V
max 0.58 U/mg, for pyruvate the K
m is 8.4×10-3 M, and V
max 0.37 U/mg. Due to these characteristics the presence of high -ketobutyrate concentrations apparently results in a l-valine, l-leucine deficiency. This in turn leads to a derepression of the AHAS synthesis from 0.03 U/mg to 0.29 U/mg and high l-isoleucine production is favoured. The derepression of the AHAS synthesis induced by the l-valine, l-leucine shortage was directly proven with a l-valine, l-leucine, l-isoleucine auxotrophic mutant where the starvation of each amino acid resulted in an increased AHAS level. This is in accordance with the fact that only one AHAS enzyme could be verified by chromatographic and electrophoretic separations as being responsible for the synthesis of all three branched-chain amino-acids. 相似文献
19.
Félix Busto Joaquin Soler Dolores de Arriaga Eduardo Cadenas 《Archives of microbiology》1984,139(2-3):255-259
Some kinetic properties of the D(-)-lactate dehydrogenase (EC 1.1.1.28) of Escherichia coli have been investigated. There were marked differences between the kinetic properties of the enzyme studied in situ compared with the in vitro D(-)-lactate dehydrogenase. D(-)-Lactate dehydrogenase in situ showed high substrate inhibition with pyruvate over the pH range 6.0–7.0, whereas the enzyme in vitro did not. The pH optimum for pyruvate reduction by the in situ D(-)-lactate dehydrogenase ranged between pH 7.5 and 7.8, whereas the in vitro enzyme showed its pH optimum between pH 6.8 and 7.0. The pK values of the prototropic groups that controlled the enzymatic activity shift to the acidic region for the in vitro enzyme with respect to the in situ enzyme. In vitro D(-)-lactate dehydrogenase exhibits homotropic interactions with its substrate, pyruvate and its coenzyme, NADH, at pH values ranging between pH 6.0 and 8.5, but the in situ enzyme showed homotropic interactions neither with pyruvate nor with NADH at all pH values studied. 相似文献
20.
In order to obtain strains of Saccharomycopsis lipolytica impaired in the active transport of l-lysine, mutants resistant to a mixture of l-canavanine, l-4-5-transdehydrolysine and l-S-amino ethylcysteine, taken either all three or two by two, were isolated. These compounds were shown previously to be competitive inhibitors of l-lysine uptake.The resistance patterns and excretion capacity of the mutants were established. All mutants behaved as monogenic. Recombination tests indicated that four genes at least were involved. All mutants were impaired in both high and low affinity l-lysine transport systems.Several hypotheses on the functions of these genes are put forward and discussed. 相似文献