Regulation of Hepatic Acetyl Coenzyme A Carboxylase by Phosphorylation and Dephosphorylation

Abstract

Partially purified acetyl-CoA carboxylase (EC 6.4.1.2) was activated several-fold by incubation with magnesium ions. The activation was inhibited by fluoride. Partially purified but not highly purified enzyme was inactivated by ATP in a reaction which was both time- and temperature-dependent. Inactivation by ATP was greatly enhanced by a protein fraction devoid of carboxylase activity, and the inactivation was independent of adenosine 3′,5′-monophosphate. Whereas inactivation of the enzyme in the presence of [γ-32P] ATP resulted in significant amounts of protein-bound 32P, incubation with [U-14C]ATP led to little incorporation of isotope into protein. The 32P label accompanied the carboxylase activity through ammonium sulfate precipitation, gel filtration, and ion exchange chromatography. The 32P-labeled carboxylase was precipitated by the antibody to homogeneous acetyl-CoA carboxylase. The evidence is consistent with a mechanism for controlling acetyl-CoA carboxylase activity by an interconversion involving phosphorylation and dephosphorylation reactions. It appears that the carboxylase protein is phosphorylated, and the activity decreased, by an ATP-dependent kinase. It is reactivated by dephosphorylation that is mediated by a magnesium-dependent phosphatase.