Increased lysolecithin acyltransferase activity in the plasma of type II hyperlipoproteinemic patients

Lecithin-cholesterol acyltransferase (LCAT) in human plasma has been shown to acylate lysolecithin to lecithin in presence of low density lipoprotein (LDL). To determine the physiological importance of LDL in activating lysolecithin acyltransferase (LAT) activity, we assayed the LAT activity in 18 hypercholesterolemic (Type II) patients and 15 control subjects. The enzyme activity was about 60% higher in the patients compared with the controls. On the other hand, the LCAT activity, measured by 2 different procedures, as well as enzyme mass, determined by radioimmuno assay, were comparable in the controls and hypercholesterolemics. The LAT activity was highly correlated with LDL levels in the plasma, but the LCAT activity and the enzyme mass had no correlation with the LDL levels. These results show that the plasma LDL is the rate-limiting activator of the enzyme, and pathological conditions, resulting in higher LDL levels, also cause higher LAT activities.