Arginine residues in the active centers of muscle pyruvate dehydrogenase.

The pyruvate dehydrogenase component isolated from the pigeon breast muscle pyruvate dehydrogenase complex is inactivated by the arginine-specific reagents, 2,3-butanedione and phenylglyoxal. The kinetics of inactivation is biphasic. The reaction order with respect to the inhibitor concentration at the fast and slow steps of the inactivation reaction is close to unity. This suggests that complete inactivation of the enzyme results from the interaction of two molecules of 2,3-butanedione or phenylglyoxal with essential groups of pyruvate dehydrogenase. In the presence of thiamine pyrophosphate and Mg2+ pyruvate protects the enzyme against inactivation. The experimental results are suggestive of the presence of two arginine residues in the substrate-binding sites of two active centres of the holoenzyme.