Branched-chain 2-oxoacid dehydrogenase kinase activity is regulated by alteration of protein thiol groups

Effects of sulfhydryl reagents (5,5'-dithiobis(2-nitrobenzoic acid) and N-ethylmaleimide) and potassium ferricyanide on the activities of branched-chain 2-oxoacid dehydrogenase complex and its kinase were studied. The dehydrogenase activity was inhibited by the sulfhydryl reagents, but not by potassium ferricyanide. The kinase activity of branched-chain 2-oxoacid dehydrogenase-kinase complex was inhibited with an increase in concentration of all three compounds. However, direct treatment of the purified kinase with N-ethylmaleimide prior to reconstitution with kinase-depleted branched-chain 2-oxoacid dehydrogenase resulted in no loss of kinase activity. These results suggest that protein thiol groups of the E2 component of the dehydrogenase complex are involved in the interaction between the dehydrogenase and its kinase.