Inhibition of Acetyl CoA Carboxylase by a High Molecular Weight Protein in Rat Liver

Acetyl CoA Carboxylase, Protein Inhibitor, Rat Liver A high molecular weight protein (approximately 1.5-2 × 106 daltons) has been found in rat liv­ er cytosol to inhibit acetyl CoA carboxylase activity. The protein inhibitor was purified by am­ monium sulfate precipitation, DEAE-cellulose chromatography and gel filtration. The inacti­ vation 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 °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.