[Determination of lecithin-cholesterol acyltransferase. Studies on the precipitation of beta-lipoproteins by dextran sulphate (author's transl)].

Uncertainties in assays of lecithin-cholesterol acyltransferase (LCAT) are generally related to the degree of isotopic equilibrium obtained by rapid exchange of unesterified cholesterol between the different lipoproteins. A new method is presented based on the precipitation of serum beta-lipoprotein with sulfated polysaccharides prior to the LCAT determination. In the absence of Beta-lipoproteins, more than 7 per cent of serum free cholesterol is esterified in the first hour and the reaction rate is linear for about 2 h. LCAT activities with normal serum expressed as cholesterol esterified per microliter mol/1/h are lower than the values reported by others. The reason for this discrepancy is that free cholesterol specific activity in total serum does not reflect the true specific activity of LCAT cholesterol substrate.