Studies on vitamin A esterase. III. The intracellular distribution of vitamin A esterase and cholesterol esterase in chicken liver

Abstract

Homogenates of chicken liver prepared in 0.25 M sucrose were fractionated by means of differential centrifugation into nuclear, mitochondrial, microsomal, and supernatant fractions. Livers of male rats were treated under identical conditions, and the cellular fractions obtained from them were used as reference. In both species, the acid phosphatase was concentrated in the mitochondrial, the glucose-6-phosphatase in the microsomal, and alkaline phosphatase in the supernatant fractions. In the rat liver vitamin A esterase, cholesterol esterase, and esterase activities were found in the microsomal fraction alone, whereas, in the chicken liver, they were distributed between the nuclear and microsomal fractions. The pattern of distribution of free and esterified cholesterol and of proteins in the various fractions was almost identical in both chicken and rat livers, e.g., esterified cholesterol was distributed between the microsomal and supernatant fractions, whereas free cholesterol was mostly in the microsomal fraction. The distribution of vitamin A ester and of vitamin A alcohol was also similar in both species: the ester was entirely in the supernatant and the alcohol was mostly in the same fraction. In chicken liver, the carotenoids were distributed evenly among the mitochondrial, microsomal, and supernatant fractions.