Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Coenzyme A”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1975

Kinetic studies on coenzyme binding and coenzyme dissociation in tryptophanase immobilized on sepharose.

The binding rate of pyridoxal '5-phosphate (Pxa-P) to apotryptophanase and the dissociation rate of the coenzyme from holotryptophanase were able to be determined by following the enzyme activity in continuous flow reactions on a column of immobilized tryptophanase. When the enzyme activity was assayed continuously in the flow system in the absence of coenzyme added to the reaction mixture, immobilized holotryptophanase lost gradually its initial activity owing to dissociation of coenzyme. The coenzyme dissociation at a given concentration of substrate (tryptophan) followed first-order kineticsmin a low substrate concentration range below the Km value, a more decreased rate constant was obtained for the coenzyme dissociation. This indicates that the coenzyme is more dissociable from the apoenzyme-coenzyme-substrate complex (ECS complex) rather than from the apoenzyme-coenzymecomplex (holoenzyme). Immobilized tryptophanase freed of coenzyme restored rapidly its original activity, when the assay mixture containing a given concentration of substrate and Pxa-P was passed through the immobilized enzyme column. The coenzyme binding at a given coenzyme concentration followed first-order kinetics, but the rate was not first order in regard to the coenzyme concentration. A plot of the reciprocal of the first-order rate constant obtained vs. the reciprocal of the coenzyme binding occurs in a two-step fashion; the first step is rapid and the second step is rate determining. Both the dissociation constant for the first step and the rate constant for the second step were shown to be independent of the substrate concentration. This means that Schiff base formation between Pxa-P and tryptophan in the assay mixture has no effect on the binding of Pxa-P to apoenzyme. The coenzyme dissociation constant at a given substrate concentration was calculated from both the rate constant of the coenzyme binding and the rate constant of the coenzyme dissociation. The values obtained by this method at different substrate concentrations were almost identical with those measured at the corresponding substrate concentrations directly by an ordinary method.

Apoenzymes↗
PubMed1984

Escherichia coli succinyl coenzyme A synthetase. Inhibition of ATP-stimulated succinate----succinyl coenzyme A exchange at low succinyl coenzyme A concentrations by an ADP trap.

The hypothesis that Escherichia coli succinyl-CoA synthetase functions by a cooperative alternating sites mechanism is based largely on the results of [18O]phosphate exchange experiments (Bild, G. S., Janson, C. A., and Boyer, P. D. (1980) J. Biol. Chem. 255, 8109-8115). In those experiments, [18O]Pi----succinate (predominantly) exchange appeared to proceed at greater rates (relative to the apparent amount of succinyl-CoA released from the enzyme) at low ATP in incubations containing ATP, CoA, succinate, [18O]Pi, 0.48 M hydroxylamine (as a succinyl-CoA trap), and a pyruvate kinase-lactate dehydrogenase ADP trap. The conclusion arrived at was that succinyl-CoA binding at one site was inversely related to ATP binding at the second site. Thus, the residence time of succinyl-CoA binding at a site would be longer at lower ATP concentrations. Our experiments show that, under the incubation conditions described by Bild et al. (Bild, G. S., Janson, C. A., and Boyer, P. D. (1980) J. Biol. Chem. 255, 8109-8115), succinyl-CoA is not efficiently trapped. Thus, at ATP concentrations from 3.6 to 150 microM, concentrations of succinyl-CoA from 13 to 78 microM were observed. Succinate----succinyl-CoA exchange reactions carried out in this range of ATP and subsaturating succinyl-CoA concentrations were found to be markedly inhibited by the addition of the ADP trap. This inhibition was more pronounced at higher ATP levels. At a saturating succinyl-CoA concentration (1.5 mM), addition of the ADP trap actually stimulated succinate----succinyl-CoA exchange. Under these conditions, ATP----Pi exchange was greatly depressed. These results are interpreted as follows. ADP is required for optimal binding of succinyl-CoA, but only when the latter is present at subsaturating concentrations; thus, the ADP trap inhibits the reaction. ATP exerts its stimulatory action on succinate---- succinyl-CoA exchange through an "other site" effect, i.e. in binding to the noncatalytic site of succinyl-CoA synthetase, it facilitates binding and release of succinyl-CoA at the catalytic site. ATP may also exert negative effects by inhibiting other site binding of ATP or by interfering with same site succinyl-CoA binding at subsaturating concentrations of the latter. These data support the notion that a half-sites mechanism applies to succinyl-CoA synthetase, but suggest that the [18O]Pi----succinate exchange data which have been instrumental in development of the cooperative alternating sites hypothesis should be re-evaluated.

Acyl Coenzyme A↗
PubMed1975

Malate dehydrogenase, circular dichroism difference spectra of porcine heart mitochondrial and supernatant enzymes, binary enzyme-coenzyme, and ternary enzyme-coenzyme-substrate analog complexes.

Circular dichroism spectra and circular dichroism difference spectra, generated when porcine heart mitochondrial and supernatant malate dehydrogenase bind coenzymes or when enzyme dihydroincotinamide nucleotide binary complexes bind substrate analogs, are presented. No significant changes are observed in protein chromophores in the 200- to 240-nm spectral range indicating that there is apparently little or no perturbation of the alpha helix or peptide backbone when binary or ternary complexes are formed. Quite different spectral perturbances occur in the two enzymes with reduced coenzyme binding as well as with substrate-analog binding by enzyme-reduced coenzyme binding. Comparison of spectral perturbations in both enzymes with oxidized or reduced coenzyme binding suggests that the dihydronicotinamide moiety of the coenzyme interacts with or perturbs indirectly the environment of aromatic amino acid residues. Reduced coenzyme binding apparently perturbs tyrosine residues in both mitochondrial malate dehydrogenase and lactic dehydrogenase. Reduced coenzyme binding perturbs tyrosine and tryptophan residues in supernatant malate dehydrogenase. The number of reduced coenzyme binding sites was determined to be two per 70,000 daltons in the mitochondrial enzyme, and the reduced coenzyme dissociation constants, determined through the change in ellipticity at 260 nm, with dihydronicotinamide adenine dinucleotide binding, were found to be good agreement with published values (Holbrook, J. J., and Wolfe, R. G. (1972) Biochemistry 11, 2499-2502) obtained through fluorescence-binding studies and indicate no apparent extra coenzyme binding sites. When D-malate forms a ternary complex with malate dehydrogenase-reduced coenzyme complexes, perturbation of both adenine and dihydronicotinamide chromophores is evident. L-Malate binding, however, apparently produces only a perturbation of the adenine chromophore in such complexes. Since the coenzyme has been found to bind in an open conformation on the surface of the enzyme and the substrate analogs bind at or very near the dihydronicotinamide moiety binding site, protein conformational changes are implicated during ternary complex formation with D-malate which can effect the adenine chromophore at some distance from the substrate binding site.

Animals↗
PubMed1982

Studies on reduced and oxidized coenzyme Q (ubiquinones). II. The determination of oxidation-reduction levels of coenzyme Q in mitochondria, microsomes and plasma by high-performance liquid chromatography.

Reduced and oxidized coenzyme Q10 (Q10H2 and Q10) in guinea-pig liver mitochondria were rapidly extracted and determined by high-performance liquid chromatography (HPLC). The percentages of Q10H2 as compared to the total (sum of Q10 and Q10H2) were increased by the addition of respiratory substrates such as succinate, malate and beta-hydroxybutyrate (State 4). The levels of Q10H2 in State 4 were increased more extensively with electron-transport inhibitors such as KCN, NaN3 and antimycin A. These results indicate that the method for determining Q10H2 and Q10 by HPLC is quite useful for investigation of the physiological function of coenzyme Q in mitochondria and other organelles. The reduced and oxidized coenzyme Q levels of rat liver mitochondria, which contain both coenzyme Q9 and coenzyme Q10, were measured simultaneously. The results suggest that coenzymes Q9 and Q10 play a similar role as an electron carriers. The liver microsomes of guinea-pig contained approx. 133 nmol total coenzyme Q10 per g protein. The Q10H2 levels of microsomes were increased from 46.5 to 67.5 and 64.8% with NADH and NADPH, respectively. The plasma levels of total coenzyme Q were 0.92 microgram/ml for man, 0.35 microgram/ml for guinea-pig and 0.27 microgram/ml for rat. The reduced coenzyme Q were also present in those plasma samples. The levels of reduced coenzyme Q were 51.1, 48.9 and 65.3%, respectively.

Animals↗
PubMed2000

The MtsA subunit of the methylthiol:coenzyme M methyltransferase of Methanosarcina barkeri catalyses both half-reactions of corrinoid-dependent dimethylsulfide: coenzyme M methyl transfer.

Methanogenesis from dimethylsulfide requires the intermediate methylation of coenzyme M. This reaction is catalyzed by a methylthiol:coenzyme M methyltransferase composed of two polypeptides, MtsA (a methylcobalamin:coenzyme M methyltransferase) and MtsB (homologous to a class of corrinoid proteins involved in methanogenesis). Recombinant MtsA was purified and found to be a homodimer that bound one zinc atom per polypeptide, but no corrinoid cofactor. MtsA is an active methylcobalamin:coenzyme M methyltransferase, but also methylates cob(I)alamin with dimethylsulfide, yielding equimolar methylcobalamin and methanethiol in an endergonic reaction with a K(eq) of 5 x 10(-)(4). MtsA and cob(I)alamin mediate dimethylsulfide:coenzyme M methyl transfer in the complete absence of MtsB. Dimethylsulfide inhibited methylcobalamin:coenzyme methyl transfer by MtsA. Inhibition by dimethylsulfide was mixed with respect to methylcobalamin, but competitive with coenzyme M. MtbA, a MtsA homolog participating in coenzyme M methylation with methylamines, was not inhibited by dimethylsulfide and did not catalyze detectable dimethylsulfide:cob(I)alamin methyl transfer. These results are most consistent with a model for the native methylthiol:coenzyme M methyltransferase in which MtsA mediates the methylation of corrinoid bound to MtsB with dimethylsulfide and subsequently demethylates MtsB-bound corrinoid with coenzyme M, possibly employing elements of the same methyltransferase active site for both reactions.

Archaeal Proteins↗
PubMed1984

Changes in the levels of endogenous coenzyme Q homologs, alpha-tocopherol, and glutathione in rat liver after hepatic ischemia and reperfusion, and the effect of pretreatment with coenzyme Q10.

The present study was undertaken to determine whether hepatic ischemia and the subsequent reflow of blood had any effect on the levels of endogenous coenzyme Q homologs, alpha-tocopherol, and glutathione, and whether coenzyme Q10 (6 mg/kg of body weight) altered these levels. Ischemia of the rat liver for 90 min resulted in decreases of 19.1 and 19.6% of endogenous alpha-tocopherol and total glutathione (GSH + GSSG) without significant changes in the levels of endogenous total coenzyme Q homologs (oxidized and reduced). Restoration of the blood flow resulted in marked decreases in endogenous coenzyme Q homologs, alpha-tocopherol, and total glutathione in the control group. In coenzyme Q10-treated animals, however, there were no changes in the levels of endogenous total coenzyme Q9, alpha-tocopherol, or total glutathione as well as in the level of the enhanced total coenzyme Q10 during the reperfusion period. On the other hand, decreases in alpha-tocopherol and total glutathione during the period of ischemia remained unchanged. These results are compatible with the assumption that cellular damage caused by hepatic ischemia can be explained by free radical reaction processes during ischemia and especially, reperfusion and suggest that exogenous coenzyme Q10 functions as an antioxidant with endogenous coenzyme Q homologs, alpha-tocopherol, and glutathione in lipid peroxidation during reperfusion.

Animals↗
PubMed2001

ATP-independent fatty acyl-coenzyme A synthesis from phospholipid: coenzyme A-dependent transacylation activity toward lysophosphatidic acid catalyzed by acyl-coenzyme A:lysophosphatidic acid acyltransferase.

CoA-dependent transacylation activity in microsomes is known to catalyze the transfer of fatty acids between phospholipids and lysophospholipids in the presence of CoA without the generation of free fatty acids. We previously found a novel acyl-CoA synthetic pathway, ATP-independent acyl-CoA synthesis from phospholipids. We proposed that: 1) the ATP-independent acyl-CoA synthesis is due to the reverse reaction of acyl-CoA:lysophospholipid acyltransferases and 2) the reverse and forward reactions of acyltransferases can combine to form a CoA-dependent transacylation system. To test these proposals, we examined whether or not recombinant mouse acyl-CoA:1-acyl-sn-glycero-3-phosphate (lysophosphatidic acid, LPA) acyltransferase (LPAAT) could catalyze ATP-independent acyl-CoA synthetic activity and CoA-dependent transacylation activity. ATP-independent acyl-CoA synthesis was indeed found in the membrane fraction from Escherichia coli cells expressing mouse LPAAT, whereas negligible activity was observed in mock-transfected cells. Phosphatidic acid (PA), but not free fatty acids, served as an acyl donor for the reaction, and LPA was formed from PA in a CoA-dependent manner during acyl-CoA synthesis. These results indicate that the ATP-independent acyl-CoA synthesis was due to the reverse reaction of LPAAT. In addition, bacterial membranes containing LPAAT catalyzed CoA-dependent acylation of LPA; PA but not free fatty acid served as an acyl donor. These results indicate that the CoA-dependent transacylation of LPA consists of 1) acyl-CoA synthesis from PA through the reverse action of LPAAT and 2) the transfer of the fatty acyl moiety of the newly formed acyl-CoA to LPA through the forward reaction of LPAAT.

Acyl Coenzyme A↗
PubMed1976

Bioenergetics in clinical medicine: prevention by forms of coenzyme Q of the inhibition by adriamycin of coenzyme Q10-enzymes in mitochondria of the myocardium.

Adriamycin inhibits the succinoxidase system and the NADH-oxidase system. Both of the intact mitocondrial enzymes and the pentane-extracted preparations are inhibited. The inhibition can be prevented by a molar ratio of coenzyme to adriamycin of 3:1 for coenzyme Q10 (ubiquinone), 5:1 for coenzyme Q7, and 5:1 for coenzyme Q4. Prevention of inhibition was observed in the decreasing order of coenzyme Q10 greater than coenzyme Q7 greater than H6 coenzyme Q4 greater than coenzyme Q4. Adriamycinone was three times more inhibitory than adriamycin, which is compatible with a less polar fragment necessary to inhibit the lipoidal coenzyme Q10. Daunomycinone was not inhibitory at a concentration at which adriamycinone is effective, indicating that the hydroxyl group of the latter could be binding at the receptor, since it should not influence electron transfer or rings B and C.

Animals↗
PubMed1995

Benzoate-coenzyme A ligase, encoded by badA, is one of three ligases able to catalyze benzoyl-coenzyme A formation during anaerobic growth of Rhodopseudomonas palustris on benzoate.

The first step of anaerobic benzoate degradation is the formation of benzoyl-coenzyme A by benzoate-coenzyme A ligase. This enzyme, purified from Rhodopseudomonas palustris, is maximally active with 5 microM benzoate. To study the molecular basis for this reaction, the benzoate-coenzyme A ligase gene (badA) was cloned and sequenced. The deduced amino acid sequence of badA showed substantial similarity to other coenzyme A ligases, with the highest degree of similarity being that to 4-hydroxybenzoate-coenzyme A ligase (50% amino acid identity) from R. palustris. A badA mutant that was constructed had barely detectable levels of ligase activity when cell extracts were assayed at 10 microM benzoate. Despite this, the mutant grew at wild-type rates on benzoate under laboratory culture conditions (3 mM benzoate), and mutant cell extracts had high levels of ligase activity when assayed at a high concentration of benzoate (1 mM). This suggested that R. palustris expresses, in addition to BadA, a benzoate-activating enzyme(s) with a relatively low affinity for benzoate. A possible role of 4-hydroxybenzoate-coenzyme A ligase (encoded by hbaA) in this capacity was investigated by constructing a badA hbaA double mutant. Although the double mutant grew more slowly on benzoate than badA cells, growth rates were still significant, suggesting the involvement of a third enzyme in benzoate activation. Competition experiments involving the addition of a small amount of cyclohexanecarboxylate to ligase assay mixtures implicated cyclohexanecarboxylate-coenzyme A ligase as being this third enzyme. These results show that wild-type R. palustris cells synthesize at least three enzymes that can catalyze the initial step in anaerobic benzoate degradation during growth on benzoate. This observation supports previous suggestions that benzoyl-coenzyme A formation plays a central role in anaerobic aromatic compound biodegradation.

Acyl Coenzyme A↗
PubMedDate not supplied

Synthesis and properties of new coenzyme mimics based on the artificial coenzyme CL4.

We have previously shown that a range of nicotinamide containing 'biomimetic coenzymes' function as active analogues of NAD+ in the oxidation of alcohols by horse liver alcohol dehydrogenase (HLADH), despite their apparently astonishing lack of structural similarity to the natural coenzyme. The simplest structure as yet shown to exhibit activity is the biomimetic coenzyme CL4. To investigate the effect of the structure of this truncated artificial coenzyme on its activity, a range of close structural analogues of CL4 were designed, synthesized and characterized. The electrochemical reduction potentials of the analogues were strongly influenced by the nature of the groups attached to the pyridine ring. All of the analogues could be chemically reduced using sodium borohydride, to give compounds with altered UV-visible absorption and fluorescence properties. An HPLC-based assay suggested that two of the new analogues were coenzymically active in the oxidation of butan-1-ol by HLADH, with one displaying a significantly higher activity than CL4. The results demonstrate which features of the structures of the coenzymes lead to desirable electrochemical and spectroscopic properties, but suggest that the structural requirements for a functional coenzyme are quite stringent. These observations may be used to design an artificial coenzyme which combines the best features of those studied so far.

Alcohol Dehydrogenase↗
PubMed1986

The effect of insulin and catecholamines on the activities of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and acyl-coenzyme A: cholesterol-o-acyltransferase in isolated rat hepatocytes.

This study was concerned with the effect of insulin and catecholamines on the rate limiting enzymes of cholesterol metabolism in rat hepatocytes. Insulin was found to increase the activity of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and to have no effect on the activity of acyl-coenzyme A: cholesterol-o-acyltransferase. Noradrenaline and isoprenaline increased the activities of both 3-hydroxy-3-methyl glutaryl coenzyme A reductase and acyl-coenzyme A: cholesterol-o-acyltransferase. The effect of noradrenaline or isoprenaline in the presence of insulin was that of a lower stimulatory response on 3-hydroxy-3-methyl glutaryl coenzyme A reductase but comparable to that found with either catecholamine alone. The combination of either catecholamine with insulin had no effect on the activity of acyl-coenzyme A: cholesterol-o-acyltransferase. These observations suggest that the activities of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and acyl-coenzyme A: cholesterol-o-acyl-transferase are regulated independently by insulin in the presence or absence of catecholamines. By contrast, catecholamines appear to regulate both enzyme activities in a similar fashion.

Animals↗