[Kinetic properties of blood plasma lecithin cholesterol acyltransferase in persons with hyper-alpha-lipoproteinemia].

A study was made of the kinetics of the lecithin-cholesterol-acyltransferase reaction (LCAT-reaction) according to the substrate, nonesterified cholesterol of high density lipoproteins (HDLP) and of the effect produced by the medium pH and apoprotein E (apo-E) on the rate of the LCAT-reaction in blood plasma of subjects with hyper-alpha-lipoproteinemia. HDLP isolated from blood plasma of subjects with hyper-alpha-lipoproteinemia were used as substrate. Infranatants obtained from blood plasma of the test subjects after removing all lipoproteins with a density of 1.21 g/ml served as a source of the enzyme. The kinetic curve of the rate of the LCAT-reaction with one or two plateaus was found to be complex in nature; pH 7.4 and 8.0 were found to be optimal for the LCAT-reaction at high and low concentrations of HDLP, respectively. At a low HDLP concentration apo-E had no remarkable effect on the rate of the LCAT-reaction, while at a high HDLP concentration the rate of the LCAT-reaction was increased. It is assumed that more than two isoforms of LCAT are present in blood plasma of subjects with hyper-alpha-lipoproteinemia.