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L Gyócsi

Publications and source records attributed to L Gyócsi.

5 recordsLinked to original sources
PubMed1982

Diacetyl: a new substrate in the overall reaction of the pyruvate dehydrogenase complex.

Pig heart pyruvate dehydrogenase complex (pyruvate: lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1) catalyzes the decomposition of diacetyl to acetate, acetyl-CoA and produces reduced NAD+ with 1:1:1 stoichiometry. The reaction rate with diacetyl is approximately 7.1% of that with pyruvate. The Km value for diacetyl was found to be 0.46 mM. Acetoin and acetaldehyde inhibit the pyruvate dehydrogenase-catalyzed reaction of diacetyl with Ki values of 0.91 mM and 0.48 mM, respectively. Inhibition patterns show that they are competitive inhibitors versus diacetyl. Acetate, as product, does not inhibit the enzymatic decomposition of diacetyl. Diacetyl is not only an alternative substrate in the pyruvate dehydrogenase reaction, but a competitive inhibitor versus pyruvate with a Ki value of 0.43 mM.

Acetaldehyde↗
PubMed1980

Interaction between the pyruvate dehydrogenase complex and citrate synthase.

Kinetic studies of the individual reaction of pig heart pyruvate dehydrogenase complex (pyruvate dehydrogenase (pyruvate:lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1); dihydrolipoamide reductase(NAD+) (NADH:lipoamide oxidoreductase, EC 1.6.4.3); dihydrolipoamide acetyltransferase (acetyl-CoA:dihydrolipoamide S-acetyltransferase, EC 2.3.1.12)), citrate synthase (citrate oxaloacetate-lyase (pro-3S-CH2COO- leads to acetyl-CoA), EC 4.1.3.7) and the pyruvate dehydrogenase complex-citrate synthase coupled system show that the KmCoA value of pyruvate dehydrogenase complex and KmCoASAc value of citrate synthase decrease in the coupled system when compared to those in the individual enzyme reactions. The explanation for this interaction may be an association between the two enzymes. When it was centrifuged with 150 000 x g for 140 min, 30% of the citrate synthase sedimented in the presence of the pyruvate dehydrogenase complex, while no sedimentation was observed in the absence of the pyruvate dehydrogenase complex. Sedimentation of cytoplasmic malate dehydrogenase, phosphotransacetylase, hemoglobin and Blue albumin were negligible under the same condition. In gel chromatography experiments a significant peak of citrate synthase activity co-migrated with the pyruvate dehydrogenase complex peak. This observation also suggests the possible association of two enzymes.

Animals↗
PubMed1978

Demonstration of a lag period in the time-course of the reaction catalyzed by pyruvate dehydrogenase complex.

At low thiamine pyrophosphate concentrations the time-course of the reaction catalyzed by mammalian pyruvate dehydrogenase complex shows a lag period of some minutes when the reaction is started by either enzyme, pyruvate or thiamine pyrophosphate. However, started by CoASH or NAD+, the lag period disappears. An increase in enzyme concentration to 25 mU/ml causes a concomitant shortening of the duration of the lag period (tau), while above this value tau is independent of the enzyme concentration. An increase in thiamine pyrophosphate concentration decreases the value of tau and the lag period vanishes at infinite thiamine pyrophosphate concentration. It is suggested that both isomerization and aggregation-dissociation reactions may play an improtant role in the development of the lag period of pyruvate dehydrogenase complex.

Animals↗
PubMed1976

Studies on the formation of acetoin from acetaldehyde by the pyruvate dehydrogenase complex and its regulation.

1. Pyruvate dehydrogenase complex was isolated from pigeon breast muscle involving steps of isoelectric precipitation, poly(ethyleneglycol) fractionation and separation on a glycerine gradient in the ultracentrifuge. 2. Arsenite, a potent inhibitor of the dihydrolipoyl transcetylase, did not affect the formation of acetoin from acetaldehyde, indicating that the pyruvate dehydrogenase component was operative in this reaction. 3. Production of acetoin by the pyruvate dehydrogenase complex is subject to regulation by phosphorylation and dephosphorylation, the dephosphorylated form only being active. 4. The inhibition by acetaldehyde of the pyruvate dehydrogenase complex could be partly explained by the formation of acetoin as an alternative reaction.

Acetaldehyde↗