Action of phospholipase D on human serum low density lipoprotein

Abstract

Phospholipase D was used to investigate the lecithin groups on the surface of serum low-density lipoprotein (LDL), isolated from normo- as well as hypercholester-emic individuals. The rate of liberation of choline from lipoprotein lecithin was studied in presence and absence of ether and in different concentrations of CaCl₂. The kinetics of the digestion in absence of ether suggested that the lecithin groups of LDL are not equally susceptible to enzymic hydrolysis. The effect of ether was to increase the susceptibility of the slowly digesting group of lecithin. Compared to LDL isolated from normal controls, LDL from hypercholesteremic individuals seemed to have a much larger fraction of lecithin that was digested at a faster rate. Immunological activity is retained in normal as well as hypercholesteremic LDL, even after hydrolysis of 75% of the total lecithin.