A Rapid Method for Lecithin: Cholesterol Actyltransferase Estimation in Human Serum

All the described procedures for lecithin: cholesterol acyltransferase (LC AT) determination in the plasma have raised criticisms: Lack of sensitivity for methods using colorimetric determination of unesterified cholesterol or phosphatidyl-choline in plasma before and after incubation at 37 °°C. Incomplete isotopic equilibrium of the free cholesterol substrate between the different lipoproteins in radioassay procedures. Gas liquid chromatography methods cannot be used when LCAT activity is low. A new method, easier, more sensitive and accurate has been developed in our laboratory: plasma samples are delipoproteinized by coprecipitation with Intralipid, dextran sulphate, and calcium chloride. Cholesterol esterification is assayed by a short incubation (30 min) of 100 µµl delipoproteinized plasma and a 30 µµl of 3H-cholesterol-labelled substrate. About 15% of cholesterol is esterified in these conditions in 30 min (35 ±± 7 µµmole/h/l). The LCAT reaction is linear for about one hour.