Interconversion of Phospho- and Dephospho- Forms of Pig Heart Pyruvate Dehydrogenase

Pyruvate dehydrogenase from pig heart exists in active and inactive forms. Interconversion from the active (dephospho) form into the inactive (phospho) form is catalyzed by an ATP-dependent kinase. Conversely the enzyme is reactivated by a phosphatase which removes the phosphate group from the protein. By gradient centrifugation pyruvate dehydrogenase was prepared free of phosphatase but still containing the kinase. Reactivation of pyruvate dehydrogenase is stimulated by adenosine 3′,5′-cyclic phosphate. There is incorporation of32P from γ -32P-ATP into the protein fraction containing the phosphatase and this phosphorylation reaction is also stimulated by adenosine 3′,5′-cyclic phosphate. The participation of this phosphate in the pyruvate dehydrogenase interconversion system suggests that, in heart muscle, pyruvate oxidation may be under hormonal control by a mechanism similar to that involved in the regulation of glycogen synthesis and breakdown.