Role of Cholesterol Esterifying Enzyme Present in the Soluble Cell Fraction of Rat Liver

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Cholesterol esterification and cholesteryl ester hydrolysis by the soluble cell fraction of the rat liver were studied in vitro.
The extent of esterification was markedly lower than that of hydrolysis, even under conditions in which the esterification rate was considerably enhanced. When cholesterol-4-¹⁴C in plasma lipoproteins was used as a substrate, the patterns of cholesteryl-¹⁴C esters synthesized by the soluble fraction were in general similar to those formed by plasma esterification. In contrast, the ¹⁴C-esters in lipoproteins did not serve as the substrate for hydrolysis. Fasting resulted in the elevation of esterification reaction by male rats, but not females. Alterations due to fasting of the radioactivity distributions among the different esters synthesized were consistent with those of the plasma transferase. The types of cholesteryl esters synthesized in liver appear to be dependent on the nutritional status of the animal.
Although the physiological significance of the soluble esterifying enzyme on maintenance of the level and composition of cholesteryl esters in situ is obscure, the results suggest that this enzyme possibly be the source of the plasma acyltransferase.