It has been reported by many investigators that phospholipids are markedly increased in atherosclerotic lesions as well as cholesterylesters. We studied the characteristics of, and the mechanisms of regulation of CDP choline: 1, 2-diacylglycerol cholinephosphotransferase (CPT) activity, one of the enzymes which synthesize phosphatidylcholine, in rat arterial wall comparing with those in rat liver.
CPT activity showed a linear relationship with incubation time and concentration of enzyme protein, upto 30 minutes and 0.1mg of protein per tube, respectively. Apparent Km value for CDP choline was 0.019mM in aorta and 0.015mM in liver. A linear activation of the enzyme was observed with upto 3.2mM of diolein in aorta and 1.6mM in liver. A maximum activity was observed around pH 8.5 in both in aorta and liver. In sub-cellular fractionaton of aorta, the highest specific activity per protein content was located in microsomal fraction.
When Ca2+, Zn2+, Cu2+ and Ba2+ were added, CPT activity was remarkably inhibited, but Mn2+ and Co2+ increased the activity in aorta in the presence of Mg2+.
CPT activity was increased by addition of a low concentration of serum. Very low density lipoprotein (VLDL) and low density lipoprotein (LDL) activated CPT activity, though high density lipoprotein (HDL) inhibited the activity. This may imply that LDL induced CPT activity in arterial wall, directly or indirectly.
CPT activity was also compared in various pathological states. Higher activity was found in hypercholesterolemic and vitamin E deficient rats than the controls. Fifty week-old rats showed significantly lower CPT activity in aorta than 4 weekolds. In spontaneous hypertansive rats, CPT activity was significantly lower in Wistar-King strain rats.
Further investigations are required in order to clarify the mechanism of regulation of CPT activity in arterial wall from the point of view of various pathological states of arterial wall.
