The substrate-mediated inactivation of the pyruvate dehydrogenase component of the pigeon breast muscle pyruvate dehydrogenase complex.

Incubation of the pyruvate dehydrogenase component isolated from the pigeon breast muscle pyruvate dehydrogenase complex with Mg2+, thiamine pyrophosphate and low concentrations of pyruvic acid in the absence of electron acceptors results in irreversible time-dependent inactivation of the enzyme. The rate of the enzyme inactivation is markedly decreased in the presence of high concentrations of pyruvate; in this case acetoin and acetolactate are detected in the reaction mixture. The enzyme activity is stabilized when the artificial electron acceptor, 2,6-dichlorophenolindophenol, is present in the reaction mixture. The substrate-mediated inactivation of the enzyme is accompanied by incorporation of the 2-[14C]-substrate fragment and labelled thiamine pyrophosphate into the protein fraction. The enzyme reactivation by neutral hydroxylamine and the protective effect of dithiothreitol suggest that the SH-group(s) may be involved in the substrate-mediated inactivation of pyruvate dehydrogenase.