Studies on vitamin A esterase. 4. The hydrolysis and synthesis of vitamin A esters by rat intestinal mucosae

Abstract

The hydrolytic and synthetic activities for vitamin A esters are present in the contents, mucosa and muscles of the small intestine, as well as in the pancreas of rats, with the luminar enzymes showing highest specific activities. Both the activities are localized in the microsomal fraction of the mucosal-cell homogenate. The activities of the mucosa can readily be brought into solution by extracting the acetone-dried mucosa with water. Hydrolysis of vitamin A acetate by the soluble enzymes did not require sodium taurocholate; that of the palmitate was very poor in the absence of the bile salt and was greatly activated by it. The hydrolytic and esterifying activities were optimum at pH 8.6 and 6.6 respectively. The hydrolytic activity was preferentially inhibited by sodium fluoride, sodium arsenite, diethylamine acetarsol, diisopropyl phosphorofluoridate and diethyl-p-nitrophenyl phosphate. Tween 20, sodium taurocholate and calcium chloride inhibited esterification alone. No coenzyme A or adenosine triphosphate appeared to be necessary for the esterification of vitamin A.