CONVERSION OF RETINOID ETHERS TO ALCOHOLS BY ENZYMATIC ACTIVITY PRESENT IN ABSTRACT: RAT LIVER MICROSOMES

An enzyme present in rat liver microsomes catalyzes the conversion of retinyl methyl ether(RME)to retinol; NADPH Is required for activity. The optimum pH for the reaction is 7.4; the K4, and V values are 120 MM RME and 14.3 nmol of retinol/mg protein/hr, respectively. As a substrate, the 2,3,6-trimethyl-4-methoxyphenyl analog of RME is as effective as RME. There is, however, no measurable activity for dealkylation of retinyl ethyl ether or retinyl butyl ether. Hepatic enzyme actlvfty for the metabolism of RME is induced by 3-methyl-cholanthrene but not by phenobarbital or RME itself. The induced activity also requires NADPH as a cofactor. The optimum pH for the induced enzyme is 8.4; the K and V, values are 50 M RME and 1 1 1 nmol of retinol/mg protein/hr, respectively. For this enzyme, RME is a better substrate than the 2,3,6-trimethyl-4-methoxyphenyl analog of RME; retinyl ethyl ether is less effective; and again, there is no measurable activity with retinyl butyl ether as a substrate