Specificity of the pyruvate dehydrogenase kinase for pyruvate dehydrogenase component bound to the surface of the kidney pyruvate dehydrogenase complex and evidence for intracore migration of pyruvate dehydrogenase component

Using the bovine kidney pyruvate dehydrogenase complex we have investigated the mechanism whereby about three pyruvate dehydrogenase (active form) kinase molecules, tightly bound to the dihydrolipoyl transacetylase core, can rapidly phosphorylate and inactivate about 20 pyruvate dehydrogenase (active form) (PDHa) tetramers which are also bound to the 60-subunit core. Evidence is presented that PDHa kinase activity is not serviced by a process of dissociation and reassociation of PDHa. Rapid inactivation of a full complement of PDHa occurs at a rate exceeding the rate of dissociation of PDHa, indicating that a PDHa must move to the fixed kinase subunits without dissociating from the dihydrolipoyl transacetylase core. Consistent with that concept, at low concentrations of complex where a significant portion of PDHa is free, bound PDHa was inactivated at a rate equivalent to that at higher concentrations of complex, and free PDHa was phosphorylated more slowly at a rate closely approximated by the rate of association of free PDHa with the transacetylase core. Thus, with a low number of PDHa molecules bound, PDHa either is preferentially positioned for phosphorylation and inactivation by PDHa kinase or can rapidly become so positioned without dissociating from the transacetylase core.