共查询到20条相似文献,搜索用时 31 毫秒
1.
Stephen P. Schiffer Michal Prochazka Peter F. Jezyk Thomas H. Roderick Marc Yudkoff Donald F. Patterson 《Biochemical genetics》1989,27(1-2):47-58
A metabolic screening program of inbred strains of mice has detected a marked organic aciduria in the BALB/cByJ strain. Gas chromatographic and mass spectrometric analysis identified large quantities ofn-butyrylglycine plus lesser quantities of ethylmalonic acid. Crosses with the nonexcreting C57BL/6J strain indicate that this condition is inherited as an autosomal recessive trait. Independently from this screening a variant with no detectable enzyme activity of butyryl CoA dehydrogenase (BCD) in liver and kidney of the BALB/cByJ strain but not other BALB/c sublines was discovered. Data from a three-point cross indicated that the null variant maps to the structural locus for the enzyme,Bcd-1, on chromosome 5. The findings indicate that a mutation at or nearBcd-1 in the BALB/cByJ strain resulted in a biochemical abnormality manifest as the BCD deficiency. It is concluded that accumulation of butyryl CoA due to a block in the oxidation of short-chain fatty acids results in an overproduction of organic metabolites leading to the observed organic aciduria. The fact that other BALB/c substrains do not exhibit this abnormality further suggests that this disorder reflects subline divergence within the BALB/c family.This work was supported by NIH Grants RR02512 and GM32592 to the University of Pennsylvania and HD23168, NS17752, and HD08536 to the Children's Hospital of Philadelphia, National Science Foundation Grant BSR 84-18828 to The Jackson Laboratory, and a Postdoctoral Fellowship from the Juvenile Diabetes Foundation International to Dr. Prochazka. 相似文献
2.
Alfons J. M. Stams Diderik R. Kremer Klaas Nicolay Gerard H. Weenk Theo A. Hansen 《Archives of microbiology》1984,139(2-3):167-173
Whole cells of Desulfobulbus propionicus fermented [1-13C]ethanol to [2-13C] and [3-13C]propionate and [1-13C]-acetate, which indicates the involvement of a randomizing pathway in the formation of propionate. Cell-free extracts prepared from cells grown on lactate (without sulfate) contained high activities of methylmalonyl-CoA: pyruvate transacetylase, acetase kinase and reasonably high activities of NAD(P)-independent L(+)-lactate dehydrogenase NAD(P)-independent pyruvate dehydrogenase, phosphotransacetylase, acetate kinase and reasonably high activity of NAD(P)-independent L(+)-lactate dehydrogenase, fumarate reductase and succinate dehydrogenase. Cell-free extracts catalyzed the conversion of succinate to propionate in the presence of pyruvate, CoA and ATP and the oxaloacetate-dependent conversion of propionate to succinate. After growth on lactate or propionate in the presence of sulfate similar enzyme levels were found except for fumarate reductase which was considerably lower. Fermentative growth on lactate led to higher cytochrome b contents than growth with sulfate as electron acceptor.The labeling studies and the enzyme measurements demonstrate that in Desulfobulbus propionate is formed via a succinate pathway involving a transcarboxylase like in Propionibacterium. The same pathway may be used for the degradation of propionate to acetate in the presence of sulfate.Abbreviations DCPIP
2,6-dichlorophenolindophenol
- PEP
phosphoenolpyruvate 相似文献
3.
d-Mannitol-1-phosphate dehydrogenase (EC 1.1.1.17) and d-mannitol dehydrogenase (EC 1.1.1.67) were estimated in a cell-free extract of the unicellular alga Platymonas subcordiformis Hazen (Prasinophyceae), d-Mannitol dehydrogenase had two activity maxima at pH 7.0 and 9.5, and a substrate specifity for d-fructose and NADH or for d-mannitol and NAD+. The K
m values were 43 mM for d-fructose and 10 mM for d-mannitol. d-Mannitol-1-phosphate dehydrogenase had a maximum activity at pH 7.5 and was specific for d-fructose 6-phosphate and NADH. The K
m value for d-fructose 6-phosphate was 5.5 mM. The reverse reaction with d-mannitol 1-phosphate as substrate could not be detected in the extract. After the addition of NaCl (up to 800 mM) to the enzyme assay, the activity of d-mannitol dehydrogenase was strongly inhibited while the activity of d-mannitol-1-phosphate dehydrogenase was enhanced. Under salt stress the K
m values of the d-mannitol dehydrogenase were shifted to higher values. The K
m value for d-fructose 6-phosphate as substrate for d-mannitol-1-phosphate dehydrogenase remained constant. Hence, it is concluded that in Platymonas the d-mannitol pool is derectly regulated via alternative pathways with different activities dependent on the osmotic pressure.Abbreviations Fru6P
d-fructose 6-phosphate
- Mes
2-(N-morpholino)ethanesulfonic acid
- MT-DH
d-mannitol-dehydrogenase
- MT1P-DH
d-mannitol-1-phosphate dehydrogenase
- Pipes
1,4-piperazinediethanesulfonic acid
- Tris
2-amino-2-(hydroxymethyl)-1,3-propanediol 相似文献
4.
83 strains ofPseudomonas aeruginosa were unable to utilizel-threonine as carbon-energy source, although this compound served as sole nitrogen source. Auxotrophs ofP. aeruginosa 9-D2 that requiredl-serine or glycine for growth could grow in the presence ofl-threonine. Extracts ofP. aeruginosa 9-D2 grown in the presence ofl-threonine contained threonine dehydrogenase and alpha-amino beta-ketobutyrate: CoA ligase activities; threonine aldolase was not detectable. Cells grown in the absence ofl-threonine produced no detectable threonine dehydrogenase.l-Leucine neither stimulated nor repressed threonine dehydrogenase levels. Glycine, and to a lesser extentl-serine, repressedl-threonine-mediated threonine dehydrogenase synthesis. A mutant of strain 9-D2 was isolated that could utilizel-threonine as sole carbon-energy source. This strain produced elevated levels of threonine dehydrogenase, but only slightly higher levels of alpha-amino beta-ketobutyrate: CoA ligase activities. 相似文献
5.
Bacteria that produced NAD+-dependent phenylalanine dehydrogenase (EC 1.4.1.20) were selected among l-methionine utilizers isolated from soil. A bacterial strain showing phenylalanine dehydrogenase activity was chosen and classified
in the genus Microbacterium. Phenylalanine dehydrogenase was purified from the crude extract of Microbacterium sp. strain DM 86-1 (TPU 3592) to homogeneity as judged by SDS-polyacrylamide disc gel electrophoresis. The enzyme has an
isoelectric point of 5.8 and a relative molecular weight (M
r) of approximately 330,000. The enzyme is composed of eight identical subunits with an M
r of approximately 41,000. The apparent K
m values for l-phenylalanine and NAD+ were calculated to be 0.10 mM and 0.20 mM, respectively. No loss of the enzyme activity was observed upon incubation at 55° C
for 10 min.
Received: 30 July 1997 / Accepted: 4 November 1997 相似文献
6.
The pathway construction and allosteric regulation of phenylalanine and tyrosine biosynthesis was examined in Neisseria gonorrhoeae. A single 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthase enzyme sensitive to feedback inhibition by l-phenylalanine was found. Chorismate mutase and prephenate dehydratase appear to co-exist as catalytic components of a bifunctional enzyme, known to be present in related genera. The latter enzyme activities were both feedback inhibited by l-phenylalanine. Prephenate dehydratase was strongly activated by l-tyrosine. NAD+-linked prephenate dehydrogenase and arogenate dehydrogenase activities coeluted following ion-exchange chromatography, suggesting their identity as catalytic properties of a single broad-specificity cyclohexadienyl dehydrogenase. Each dehydrogenase activity was inhibited by 4-hydroxyphenylpyruvate, but not by l-tyrosine. Two aromatic aminotransferases were resolved, one preferring the l-phenylalanine:2-ketoglutarate substrate combination and the other preferring the l-tyrosine: 2-ketoglutarate substrate combination. Each aminotransferase was also able to transaminate prephenate. The overall picture of regulation is one in which l-tyrosine modulates l-phenylalanine synthesis via activation of prephenate dehydratase. l-Phenylalanine in turn regulates early-pathway flow through inhibition of DAHP synthase. The recent phylogenetic positioning of N. gonorrhoeae makes it a key reference organism for emerging interpretations about aromatic-pathway evolution. 相似文献
7.
Terumi Saito Tetsuya Fukui Fumiaki Ikeda Yoshimasa Tanaka Kenkichi Tomita 《Archives of microbiology》1977,114(3):211-217
Zoogloea ramigera I-16-M was found to contain two stereospecific acetoacetyl CoA reductases; one was NADP+-linked and d(-)--hydroxybutyryl CoA specific and the other was NAD+-linked and l(+)-isomer specific. The NADP+-linked enzyme, purified approximately 150-fold, had a pH optimum for the reduction of acetoacetyl CoA at 8.1, but no definite pH optimum for the oxidation of -hydroxybutyryl CoA. The apparent Michaelis constants for acetoacetyl CoA and NADPH were 8.3 and 21 M, respectively. The enzyme was markedly inhibited by acetoacetyl CoA at concentrations higher than 10 M.The incorporation of [1-14C]acetyl CoA into poly--hydroxybutyrate (PHB) by bacterial crude extract (containing -ketothiolase, acetoacetyl CoA reductases, enoyl CoA hydratases and PHB synthases) or by a system reconstituted from purified preparations of -ketothiolase, acetoacetyl CoA reductase and PHB synthase, was observed only in the presence of NADPH, but not NADH. Among various enzymes involved in PHB metabolism, only the specific activity of glucose 6-phosphate dehydrogenase was elevated 5-fold within 2 h after the addition of glucose to the cells grown in the basal medium.These findings suggest that, in Z. ramigera I-16-M, acetoacetyl CoA is directly reduced to d(-)--hydroxybutyryl CoA by the NADP+-dependent reductase, and PHB synthesis is at least partially controled by NADPH availability through glucose 6-phosphate dehydrogenase.Non-Standard Abbreviation PHB
poly--hydroxybutyrate 相似文献
8.
Anne Siri Langelandsvik I. H. Steen Nils-Kåre Birkeland Torleiv Lien 《Archives of microbiology》1997,168(1):59-67
A thermostable l-malate dehydrogenase from the hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus was isolated and characterized, and its gene was cloned and sequenced. The enzyme is a homodimer with a molecular mass of
70 kDa and catalyzes preferentially the reduction of oxaloacetic acid with NADH. A. fulgidus
l-malate dehydrogenase was stable for 5 h at 90° C, and the half-life at 101° C was 80 min. Thus, A. fulgidus
l-malate dehydrogenase is the most thermostable l-malate dehydrogenase characterized to date. Addition of K2HPO4 (1 M) increased the thermal stability by 40%. The primary structure shows a high similarity to l-lactate dehydrogenase from Thermotoga maritima and gram-positive bacteria, and to l-malate dehydrogenase from the archaeon Haloarcula marismortui and other l-lactate-dehydrogenase-like l-malate dehydrogenases.
Received: 20 November 1997 / Accepted: 28 February 1997 相似文献
9.
Mark R. Smith W. J. J. van den Tweel Jan A. M. de Bont 《Applied microbiology and biotechnology》1991,36(2):246-251
Summary Both stereoisomers of 3-chloro-2-methylpropionic acid (CMPA) and its methyl esters (MeCMPA) serve as growth substrates for a bacterial isolate (Xanthobacter sp. CIMW 99) when supplied as sole source of carbon and energy. Biodegradation of dl-CMPA and dl-MeCMPA was shown to be via a common pathway; an initial, constitutive, esterase converted the methyl ester to the corresponding carboxylic acid. Further metabolism required the activation of CMPA involving a CoA-, ATP-, Mg2+-dependent chloroacyl-CoA synthetase. Most noteworthy, it was the product of this reaction (3-chloro-2-methylpropionyl-CoA) that underwent hydrolytic dehalogenation to give 3-hydroxy-2-methylpropionyl-CoA (3-hydroxyisobutyryl-CoA). Further biodegradation proceeded by the action of a dehydrogenase on the CoA derivative to give methylmalonate-CoA-semialdahyde. Cells of CIMW 99 also contained a stable, constitutive, highly active 3-hydroxyisobutyrate dehydrogenase that was specific for the l(+) isomer. However, evidence is presented suggesting that this enzyme was not involved in the catabolism of the chlorinated substrates.
Offprint requests to: M. R. Smith 相似文献
10.
d-Xylulose-forming d-arabitol dehydrogenase (aArDH) is a key enzyme in the bio-conversion of d-arabitol to xylitol. In this study, we cloned the NAD-dependent d-xylulose-forming d-arabitol dehydrogenase gene from an acetic acid bacterium, Acetobacter suboxydans sp. The enzyme was purified from A. suboxydans sp. and was heterogeneously expressed in Escherichia coli. The native or recombinant enzyme was preferred NAD(H) to NADP(H) as coenzyme. The active recombinant aArDH expressed in
E. coli is a homodimer, whereas the native aArDH in A. suboxydans is a homotetramer. On SDS–PAGE, the recombinant and native aArDH give one protein band at the position corresponding to 28 kDa.
The optimum pH of polyol oxidation and ketone reduction is found to be pH 8.5 and 5.5 respectively. The highest reaction rate
is observed when d-arabitol is used as the substrate (K
m = 4.5 mM) and the product is determined to be d-xylulose by HPLC analysis. 相似文献
11.
A newly isolated gram-negative bacterium, possibly Brevundimonas diminuta, utilised d,l-vanillylmandelate (d,l-VMA) as a sole carbon and energy source. The organism converted d,l-VMA to vanillylglyoxylate using a soluble NAD-dependent dehydrogenase specific for d-VMA and a dye-linked, membrane-associated l-VMA dehydrogenase. Vanillylglyoxylate was further metabolised by decarboxylation, dehydrogenation and demethylation to protocatechuate.
A 4,5-dioxygenase cleaved protocatechuate to 2-hydroxy-4-carboxymuconic semialdehyde. Partially purified d-VMA dehydrogenase exhibited optimal activity at 30° C and pH 9.5 and had an apparent K
m for d-VMA of 470 μM. Although induced by several substituted mandelates, the enzyme had a narrow substrate specificity range with
virtually no activity towards d-mandelate. Such properties render the enzyme of potential use in both diagnostic and biosynthetic applications.
Received: 23 January 1996 / Accepted: 9 April 1996 相似文献
12.
Fekete E Karaffa L Sándor E Bányai I Seiboth B Gyémánt G Sepsi A Szentirmai A Kubicek CP 《Archives of microbiology》2004,181(1):35-44
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
13.
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
14.
Gluconobacter oxydans LMG 1489 was selected as the best strain for NAD(P)-dependent polyol dehydrogenase production. The highest enzyme activities were obtained when this strain was cultivated on a medium consisting of 30 g glycerol l–1, 7.2 g peptone l–1 and 1.8 g yeast extract l–1. Two D-fructose reducing, NAD-dependent intracellular enzymes were present in the G. oxydans cell-free extract: sorbitol dehydrogenase, and mannitol dehydrogenase. Substrate reduction occurred optimally at a low pH (pH 6), while the optimum for substrate oxidation was situated at alkaline pHs (pH 9.5–10.5). The mannitol dehydrogenase was more thermostable than the sorbitol dehydrogenase. The cell-free extract could be used to produce D-mannitol and D-sorbitol enzymatically from D-fructose. Efficient coenzyme regeneration was accomplished by formate dehydrogenase-mediated oxidation of formate into CO2. 相似文献
15.
Bhuiya MW Sakuraba H Kujo C Nunoura-Kominato N Kawarabayasi Y Kikuchi H Ohshima T 《Extremophiles : life under extreme conditions》2000,4(6):333-341
NADP-dependent glutamate dehydrogenase (l-glutamate: NADP oxidoreductase, deaminating, EC 1.4.1.4) from the aerobic hyperthermophilic archaeon Aeropyrum pernix K1 (JCM 9820) was purified to homogeneity for characterization. The enzyme retained its full activity on heating at 95°C
for 30 min, and the maximum activity in l-glutamate deamination was obtained around 100°C. The enzyme showed a strict specificity for l-glutamate and NADP on oxidative deamination and for 2-oxoglutarate and NADPH on reductive amination. The K
m values for NADP, l-glutamate, NADPH, 2-oxoglutarate, and ammonia were 0.039, 3.3, 0.022, 1.7, and 83 mM, respectively. On the basis of the N-terminal
amino acid sequence, the encoding gene was identified in the A. pernix K1 genome, cloned, and expressed in Escherichia coli. Analysis of the nucleotide sequence revealed an open reading frame of 1257 bp starting with a minor TTG codon and encoding
a protein of 418 amino acids with a molecular weight of 46 170. Phylogenetic analysis revealed that the glutamate dehydrogenase
from A. pernix K1 clustered with those from aerobic Sulfolobus solfataricus, Sulfolobus shibatae, and anaerobic Pyrobaculum islandicum in Crenarchaeota, and it separated from another cluster of the enzyme from Thermococcales in Euryarchaeota. The branching pattern of the enzymes from A. pernix K1, S. solfataricus, S. shibatae, and Pb. islandicum in the phylogenetic tree coincided with that of 16S rDNAs obtained from the same organisms.
Received: April 24, 2000 / Accepted: August 10, 2000 相似文献
16.
Werner Hummel Horst Schütte Elke Schmidt Christian Wandrey Maria-Regina Kula 《Applied microbiology and biotechnology》1987,26(5):409-416
Summary
l-Phenylalanine dehydrogenase [l-phenylalanine: NAD+-oxidoreductase (deaminating)] of Rhodococcus sp. strain M4 was studied emphasizing its application for the production of l-phenylalanine. A high enzyme level (30,000 U·l-1, 25–30 U·mg-1 in the crude extract) could be reached during aerob degradation of l-phenylalanine (10 g·l-1) under optimized growth coditions. A partial purification of the intracellular enzyme by liquid-liquid extraction, and DEAE-cellulose led to a specific activity of more than 1300 U·mg-1. The continuous production of l-phenylalanine in an enzyme-membrane-reactor for 350h resulted in a space-time yield of 456 g·l-1·d-1 with a mean substrate conversion of 95%. Consumption of phenylalanine dehydrogenase was 1,500 U·kg Phe-1.Abbreviations BSA
bovine serum albumine
- pheDH
l-phenylalanine dehydrogenase
- phepyr
phenylpyruvate
- OD
optical density
- FDH
formate dehydrogenase 相似文献
17.
18.
Werner Hummel Horst Schütte Elke Schmidt Maria-Regina Kula 《Applied microbiology and biotechnology》1987,27(3):283-291
Summary A new acylase catalyzing the deacetylation of acetamidocinnamic acid (ACA) was found in strains of Brevibacterium sp. Such strains could be isolated from soil samples by their ability to grow on ACA as well as on l-phenylalanine. A 110-fold enrichment of the enzyme with an over-all yield of 48% was obtained in 4 steps resulting in an electrophoretically pure preparation of 28.6 U·mg-1. Important enzymological data concerning the application of the enzyme are: K
M (ACA) 0.45 mM, pH-optimum 7.5, heat stability up to 52°C, molecular weight of 50.000 Dalton, two subunits. Deacetylation of ACA resulted in phenylpyruvate via the unstable enamine-imine derivative. Coupling the acylase with l-phenylalanine dehydrogenase proved to be an alternative route for l-phenylalanine production avoiding substrate inhibition by phenylpyruvate and its instability. The substrate specifity of ACA-acylase revealed that the enzyme probably acts as a dipeptidase in its biological function.Abbreviations ACA
acetamidocinnamate, acetamidocinnamic acid
- FPLC
fast protein liquid chromatography
- pheDH
l-Phenylalanine dehydrogenase
- HicDH
Hydroxyisocaproate dehydrogenase
- OD
optical density
- BSA
bovine serum albumin
- FDH
formate dehydrogenase
Dedicated to Professor Dr. H. J. Rehm on the occasion of his 60th birthday 相似文献
19.
In Nocardia sp. 239 d-phenylalanine is converted into l-phenylalanine by an inducible amino acid racemase. The further catabolism of this amino acid involves an NAD-dependent l-phenylalanine dehydrogenase. This enzyme was detected only in cells grown on l- or d-phenylalanine and in batch cultures highest activities were obtained at relatively low amino acid concentrations in the medium. The presence of additional carbon- or nitrogen sources invariably resulted in decreased enzyme levels. From experiments with phenylalanine-limited continuous cultures it appeared that the rate of synthesis of the enzyme increased with increasing growth rates. The regulation of phenylalanine dehydrogenase synthesis was studied in more detail during growth of the organism on mixtures of methanol and l-phenylalanine. Highest rates of l-phenylalanine dehydrogenase production were observed with increasing ratios of l-phenylalanine/methanol in the feed of chemostat cultures. Characteristic properties of the enzyme were investigated following its (partial) purification from l- and d-phenylalanine-grown cells. This resulted in the isolation of enzymes with identical properties. The native enzyme had a molecular weight of 42 000 and consisted of a single subunit; it showed activity with l-phenylalanine, phenylpyruvate, 4-hydroxyphenyl-pyruvate, indole-3-pyruvate and -ketoisocaproate, but not with imidazolepyruvate, d-phenylalanine and other l-amino acids tested. Maximum activities with phenylpyruvate (310 mol min-1 mg-1 of purified protein) were observed at pH 10 and 53°C. Sorbitol and glycerol stabilized the enzyme.Abbreviations RuMP
ribulose monophosphate
- HPS
hexulose-6-phosphate synthase
- HPT
hexulose-6-phosphate isomerase
- FPLC
fast protein liquid chromatography 相似文献
20.
A simple procedure for the preparation of soluble human succinate dehydrogenase is described. These preparations have proved suitable for analysis by zone electrophoresis, using a specific stain to detect activity after separation. In a survey of succinate dehydrogenase from various tissues and different individuals, no evidence for genetic heterogeneity due to the expression of either multiple loci or alternative alleles at the succinate dehydrogenase locus was found. However, epigenetic heterogeneity in both molecular size and charge was seen and various explanations for the occurrence of the isoenzymes are explored. Estimates of molecular size (93,300 ± 9100) suggest that the smallest active unit of succinate dehydrogenase accounts for the major part of the solubilized activity. Kinetic studies have shown that the apparent K
m
values for succinate (0.9mm) and PMS (0.4mm) are comparable to those previously described for the beef heart enzyme, and these parameters were not significantly altered when the enzyme was removed from the membrane milieu. However a marked non-succinate-dependent activation of the membrane-associated enzyme at 38C is apparently lost on solubilization, and this observation may have some bearing on earlier reports of an apparent decrease in V
max on solubilization of succinate dehydrogenase. 相似文献