Evidence for the Presence in Human Plasma of Lecithin: Cholesterol Acyltransferase Activity (β‐LCAT) Specifically Esterifying Free Cholesterol of Combined Pre‐β‐ and β‐Lipoproteins: Studies of Fish Eye Disease Patients and Control Subjects

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Abstract
The present study was undertaken to test our hypothesis that two different lecithin: cholesterol acyltransferase (LCAT) activities exist in normal human plasma, one denoted α‐LCAT esterifying the free cholesterol of high density lipoproteins (HDL) and the other denoted β‐LCAT acting on the free cholesterol of very low (VLDL) and low (LDL) density lipoproteins. Plasmas depleted of HDL were obtained by means of preparative ultracentrifugation. Incubation at 37°C of these plasma fractions from control subjects and patients with fish eye disease resulted in esterification of the remaining free cholesterol of combined VLDL and LDL (pre‐β‐ and β‐lipoproteins) in the HDL depleted plasmas. The shapes of the cholesterol esterification rate curves were similar for whole and HDL depleted plasmas from both control subjects and fish eye disease patients. In crosswise mixed incubation experiments with isolated combined VLD and LDL and total lipoprotein depleted plasma from a control subject and a patient with fish eye disease, respectively, esterification of free cholesterol occurred. Incubation of isolated total lipoproteins in plasma from a patient with LCAT deficiency mixed with total lipoprotein depleted plasma from a fish eye disease patient as a source of LCAT caused cholesterol esterification but did not result in normalization of the LCAT deficiency HDL particles, while the amount of normal‐sized LDL particles increased. The present results support the hypothesis that β‐LCAT exists in normal human plasma.

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