Regulation of ACAT
Cellular cholesteryl esters are the products of acyl-CoA: cholesterol acyltransferase (ACAT). The enzyme can be isolated from tissue or cellular homogenates with the microsomal fraction and its activity determined. The liver microsomal fraction, isolated by standard techniques, consists mainly of two vesicle populations: those derived from plasma membrane and those derived from endoplasmic reticular membranes (rough and smooth). The major part of non-esterified cholesterol present in the microsomal fraction is associated with plasma membrane vesicles, whereas ACAT is associated with vesicles derived from rough endoplasmic reticular membranes (Balasubramaniam et al. 1978). “Activity” in the microsomal fraction is assayed under optimal conditions with respect to acyl-CoA but at the concentration of non-esterified cholesterol in the environment of the enzyme in endoplasmic reticular membrane vesicles. The rate at which this activity changes can, hence, be useful as an index of the rate at which cholesterol gets transferred to the immediate environment of the enzyme.
KeywordsCholesterol Progesterone NADPH Cytosol Oleate
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