Hydrolysis of Retinol Palmitate by Rat Liver

From the ¹ From the Institute of Nutrition Sciences, Columbia University, New York, New York 10032

Retinol acetate hydrolase is localized in rat liver microsomes whereas the retinol palmitate-hydrolyzing activity was found in the nuclear and in the mitochondrial lysosome-rich fractions. Acetone-dried powder from whole rat liver retained all of its retinol palmitate-hydrolyzing activity. Ammonium sulfate fractionation of the acetone-dried powder yielded a partially purified enzyme liberating 240 mµmoles of retinol per mg of protein per 60 min when retinol palmitate was used as substrate. The pH optimum was 8.6 and K_m was 1.6 x 10^-4 m. The enzyme was inhibited by ethanol, acetone, and Tween 80 and activated by bile salts. The activity of the enzyme was greatest for retinol palmitate, 60% lower for retinol acetate, and 70 to 90% lower for retinol oleate, linoleate, linolenate, stearate, myristate, and laurate. The liver enzyme efficiently hydrolyzed the retinol ester stored in the liver.

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