CHOLESTEROL-ESTERIFYING ACTIVITY OF CELL-FREE PREPARATIONS OF RABBIT PERITONEAL MACROPHAGES

Cell-free preparations of rabbit peritoneal macrophages were used to study the properties of the cholesterol-esterifying enzymes present in these cells. Incubation of 14C-labelled cholesterol and oleic acid with dialysed cell-free preparations resulted in the formation of 14C-labelled cholesterol ester without any requirement for ATP or CoASH. The optimum pH for the cholesterol-esterifying enzyme activity in the peritoneal homogenates was pH 6.3. In order to investigate the mechanism of the reaction, [1-14C]oleic acid and lecithin labelled in the β-position with [1-14C]oleic acid were in turn incubated with the homogenate in the presence of unlabelled cholesterol. Since the unesterified fatty acid, but not that combined as lecithin, was incorporated into cholesterol ester, it was concluded that the reaction does not proceed via a transesterification reaction, but by the direct esterification of cholesterol with free fatty acid. © 1969.