A new method for the isolation of rat liver acetyl-CoA carboxylase

Rat liver acetyl-CoA carboxylase has been purified to homogeneity by a new method involving polyethylene glycol precipitation, and DEAE and Sepharose 4B chromatography. The final product displays a single band on SDS polyacrylamide gel electrophoresis of estimated molecular weight 240,000. This material contains 5.5 +/- 0.3 moles of alkali-labile phosphate per subunit and has a specific activity of 1.2 +/- 0.2 units per mg protein. As compared to previous purification procedures for the liver enzyme, this product has a higher phosphate content, lower specific activity, and an absence of major proteolysis. Trypsin digestion of 32P-labeled acetyl-CoA carboxylase from hepatocytes reveals that the 32P-labeled phosphorylation sites are extremely labile to proteolytic digestion. Potential modification of isolated liver acetyl-CoA carboxylase by proteolysis and/or dephosphorylation must be ascertained prior to in vitro enzymatic studies.