RE-EVALUATION OF PROPERTIES OF ACETYL-COA CARBOXYLASE FROM RAT-LIVER

Abstract

Rat liver acetyl-CoA carboxylase can be rapidly isolated by a new procedure which uses avidin-Sepharose affinity chromatography. The isolated enzyme has MW = 260,000; none or very little of the proteolytic products of the carboxylase which are formed in conventional purification procedures are found in these preparations. Apparently the previously reported subunit of the carboxylase, with MW = 230,000, is itself the product of proteolysis. The properties of the enzyme produced by this new method are quite different from those of the conventionally prepared enzyme. This enzyme contains 6 mol of alkali-labile phosphate/mol of subunit, rather than 2 mol; the Km for acetyl-CoA is .apprx. 8-fold higher and the specific activity is only .apprx. 1/5 of that previously reported. The large amount of phosphate does not appear to cause the low specific activity of the new enzyme preparation, because alkaline phosphatase treatment reduces the number of phosphates/subunit from 6-3 mol but does not change the specific activity.