The esterification of cholesterol in vitro by rat plasma

The synthesis of cholesterol esters by plasma and extracts of acetone powders of rat plasma was studied with the following substrates: (a) lecithin labeled in the β position with either [I-¹⁴C]oleic acid, [I-¹⁴C]linoleic acid or [I-¹⁴C]palmitic acid; (b) trigylcerides labeled with either [I-¹⁴C]palmitic acid or [I-¹⁴]oleic acid; (c) [4-¹⁴C]cholesterol. As much as 24 and 50% of the incubated ¹⁴C was recovered as cholesterol esters when the labeled lecithins and free cholesterol, respectively, were incubated, and less than I% was so recovered when the labeled trigylcerides served as substrates. Snake venom completely prevented the formation of labeled cholesterol esters by acetone powder extracts in the experiments with fatty acid-labelled lecithin and the labeled free cholesterol. These findings support the hypothesis that the esterification of cholesterol is brought about by a fatty acid transferase and, in addition, suggest that the transesterification is limited to fatty acidss on the β position of phospholipids, regardless of the nature of the fatty acids, this being an intermediatry step even in the transesterification from trigylcerides.