Hydrolysis of Ketinol Palmitate by Rat Liver*

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 mpmoles of retinol per mg of protein per 60 min when retinol palmitate was used as substrate. The pH optimum was 8.6 and Km was 1.6 X lO+ 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.