Reversible ATP-dependent inactivation of adipose diacylglycerol acyltransferase

Diacylglycerol acyltransferase from rat adipose tissue is shown to be inactivated by 30 to 40% upon incubation with adenosine 5′-triphosphate (ATP) and Mg²⁺. The activity responsible for this inactivation is associated with the cytosolic fraction, specific for ATP, prevented when ATP is substituted by β,γ-methylene-ATP, and partially blocked by 1 mM ethylenediaminetetraacetate or 40 mM NaF, but not by inhibitors of adenosine 3′,5′-cyclic-monophosphate (cAMP)-dependent protein kinase and/or protein kinase C (PKC). The cytosolic activity cannot be mimicked by (cAMP)-protein kinase nor by PKC. Inactivated diacylglycerol acyltransferase from ATP/cytosol-treated microsomes can be reactivated by incubation with partially purified protein phosphate from rat liver, and can be inactivated again by further addition of ATP in the presence of cytosol. The results suggest the existence in adipose tissue of a protein kinase other than cAMP-protein kinase or PKC, which may be involved in the regulation of triacylglycerol synthesis.