Substrate-dependent inactivation of muscle pyruvate dehydrogenase: identification of the acetyl-substituted enzyme form.

The properties of the pyruvate dehydrogenase component isolated from the pigeon breast muscle pyruvate dehydrogenase complex were studied upon inactivation of the enzyme in an incomplete reaction mixture: in the presence of cofactors and pyruvate, and in the absence of electron acceptors. The substrate-dependent inactivation was shown to result in the modification of two sulfhydryl groups per mole of the enzyme, in the appearance of a maximum at 235 nm in the protein absorption spectrum, and in the involvement of 1.5 moles of the [2-14C]-pyruvate fragment per mole of the pyruvate dehydrogenase. The fragment-protein bond is acid-stable, labile in alkali, and breaks up in the presence of performic acid, neutral hydroxylamine and dithiothreitol. An acetyl-substituted form of pyruvate dehydrogenase appearing with the participation of sulfhydryl enzyme groups is suggested.