Inhibition of acetyl CoA carboxylase by a high molecular weight protein in rat liver.

A high molecular weight protein (approximately 1.5--2 x 10(6) daltons) has been found in rat liver cytosol to inhibit acetyl CoA carboxylase activity. The protein inhibitor was purified by ammonium sulfate precipitation, DEAE-cellulose chromatography and gel filtration. The inactivation of the carboxylase is not attributable to either phosphorylation of the enzyme or to action on substrates or cofactors of the reaction. The activity of the inhibitor is destroyed by heating to 55 degrees C for 5 min, by treatment with trypsin, or by increasing bovine serum albumin in the reaction mixture. Hence it appears that the inhibitor is a regulatory protein that acts directly on acetyl CoA carboxylase.