ENZYMES OF KETOGENESIS IN BOVINE RUMEN EPITHELIUM

Abstract

The activities of various enzymes involved in formation of acetoacetate from acetoacetyl-coenzyme A (acetoacetyl-CoA) were investigated using crude extracts of rumen papillae. Acetoacetyl-CoA deacylase and 3-hydroxy-3-methylglutaryl-CoA synthase were measurable in these extracts, but addition of succinate (15 mM) produced an increased activity of acetoacetyl-CoA removal which was up to threefold, or more, that of deacylase. Succinyl-CoA was identified as a product of the reaction in the presence of succinate, indicating that 3-oxo acid CoA transferase was present in the papillae. The maximum activities of synthase, deacylase, and transferase were 16, 14, and 70% of the total capacity to remove acetoacetyl-CoA, respectively. The possible physiological significance of the participation of 3-oxo acid CoA transferase in ketogenesis in rumen epithelium was discussed.