Acetyl Coenzyme A Carboxylase. Rapid Purification of the Chick Liver Enzyme and Steady State Kinetic Analysis of the Carboxylase-catalyzed Reaction

Avidin affinity chromatography was used to rapidly purify acetyl-CoA carboxylase to homogeneity in high yield from chicken liver. Dissociation of the purified carboxylase with dodecyl sulfate yielded a single size class of subunit polypeptide of 225,000 daltons. A steady state kinetic analysis of the carboxylase-catalyzed carboxylation of acetyl-CoA gave rise to intersecting line patterns in all double-reciprocal plots of initial velocity with each substrate pair, i.e. ATP . Mg and HCO3(-) and acetyl-CoA. It was concluded that the kinetic mechanism involves a quaternary complex of the enzyme, ADP, Pi, and acetyl-CoA rather than a double displacement as previously believed. The ordered addition of ATP, HCO3(-), and then acetyl-CoA, to the citrate-activated form of the carboxylase is the kinetic mechanism most consistent with the results.