Dependence of human plasma lecithin:cholesterol acyltransferase activity upon high-density lipoproteins.

The conclusion that HDL2 suppress lecithin:cholesterol acyltransferase activity has been re-examined using three assay methods. Removal by ultracentrifugation of lipoproteins of d 1.125 g/ml reduced activity to 53% (n = 15) of control plasma. Replacement of VLDL and LDL was without effect, but addition of HDL2 restored activity. Addition of HDL2 to d 1.125 g/ml infranate in quantities greater than had been present in original plasma had no further effect on activity, and addition of HDL2 to plasma had no effect on activity. It is concluded that HDL2 are required for full expression of plasma lecithin:cholesterol acyltransferase activity.