Acta Biochimica et Biophysica 13. (1978)
1978 / 3. szám - Alkonyi, I.-Bolygó, E.-Gyócsi, L.-Sümegi, B.: Kinetic Studies of the Inhibitory Effect of Acetaldehyde and D(-)Acetion on the Pyruvate Dehydrogenase Complex from Pig Heart
Acta Biochim. et Biophys. Acad. Sei. Hung. Vol. 13 (3), pp. 143—152 (1978) Kinetic Studies of the Inhibitory Effect of Acetaldehyde and D(-)Acetoin on the Pyruvate Dehydrogenase Complex from Pig Heart I. Alkonyi, E. Bolygó, L. Gyócsi, В. Sümegi Institute of Biochemistry, University Medical School, Pécs, Hungary (Received January 26, 1978) Inhibition of the pyruvate dehydrogenase complex (purified from pig heart) by acetaldehyde and D(— )acetoin was shown to be due to the inhibition of the pyruvate dehydrogenase component of the complex. Kinetic analysis showed that inhibition by acetaldehyde is uncompetitive versus pyruvate, Co A, NAD+ and that inhibition by D(—)acetoin is competitive versus pyruvate but uncompetitive versus CoA and NAD+. A theoretical treatment of the mechanism of these inhibitions is presented. Cysteine partly counteracted the inhibitory effect of acetaldehyde by lowering its concentration through a chemical reaction. The mammalian pyruvate dehydrogenase complex catalyzes a co-ordinated sequence of reactions that can be represented by : pyruvate + CoA + NAD+_-> acetyl-CoA + C02 + NADH + H+ (1) This reaction is catalyzed by three enzymes, pyruvate dehydrogenase (E,), lipoate acetyltransferase (E2) and lipoamide dehydrogenase (E3) (Koike et ah, 1963; Hayakawa et ah, 1969; Barrera et al. 1972; Hucho, 1975). It has been observed that low concentrations of acetaldehyde and D(-)acetoin effectively inhibit the overall reaction of the pyruvate dehydrogenase complex from different types of mammalian tissue (Blass, Lewis, 1973; Cooper et ah, 1974), but the precise mechanism of these inhibitions has not been elucidated. It has been found (Jagannathan, Schweet, 1952; Juni, Heym, 1956; Breslow, 1958), that under certain conditions the enzyme-HEtTPP complex formed during the decarboxylation of pyruvate reacts with acetaldehyde to form acetoin in mammalian organs. In a recent paper we reported that the inhibition caused by acetaldehyde and the amount of acetoin formed concomitantly varied in a monotonous way (Alkonyi et ah, 1976). The aim of the present work was to clarify the mechanism of both inhibitions (by acetaldehyde and by D(-)acetoin, respectively) and to elucidate the connection between acetoin formation and inhibition of the pyruvate dehydrogenase complex by acetaldehyde. Abbreviations : TPP, thiamine pyrophosphate; HEtTPP, hydroxyethyliamine pyrophosphate Acta Biochimica et Biophysica Academiae Scientiarum Hungaricae 13, 1978