Lecithin:cholesterol acyltransferase (LCAT) mass; its relationship to LCAT activity and cholesterol esterification rate.

The relationship between plasma 1ecithin:cho- lesterol acyltransferase mass and enzyme activity and be- tween mass and plasma cholesterol esterification rate was determined in 25 adult volunteers without overt disease (14 normolipidemic and 11 hyperlipidemic). Furthermore, the relationship of 1ecithin:cholesterol acyltransferase mass and cholesterol esterification rate to lipids, apoproteins, age, and ideal body weight was assessed. Lecithin:cholesterol acyl- transferase, mass determined by radioimmunoassay was highly correlated with enzyme activity assayed using a heated plasma substrate (r = 0.636) and with the molar cholesterol esterification rate determined either by radioassay (r = 0.809) or by measurement of the decrease of unesterified cho- lesterol (r = 0.62 1). Lecithin:cholesterol acyltransferase mass was also positively correlated with total cholesterol (r = 0.608), unesterified cholesterol (r = 0.562), age (r = 0.544), and percent ideal body weight (r = 0.619), but was not significantly correlated with log triglyceride, high den- sity lipoprotein cholesterol, or apolipoproteins A-I, A-11, or D. Plasma cholesterol esterification rate by both methods was highly positively correlated with total cholesterol, un- esterified cholesterol, log triglyceride, and age, but was in- versely correlated with high density lipoprotein cholesterol. Upon partial correlation analysis with 1ecithin:cholesterol acyltransferase mass kept constant the cholesterol esterifica- tion rate remained significantly positively related to total cholesterol, unesterified cholesterol, and log triglyceride and inversely related to high density lipoprotein cholesterol. Two subjects had normal 1ecithin:cholesterol acyltransferase but approximately half normal molar cholesterol esterification ra1e.m Measurement of 1ecithin:choles-