Retinoic acid 5,6-epoxidase. Properties and biological significance.

A retinoic acid epoxidase is present in rat kidney homogenates. It is found in the particulate fraction, and is dependent on ATP, NADPH, and oxygen. It is stimulated by Fe2+ and inhibited by Mn2+, Zn2+, Cu2+, EDTA, and N,N'-diphenyl-para-phenylenediamine. Its properties are closest to those of microsomal lipid peroxidases previously studied. Epoxidase activity is not affected by the rat's vitamin A status, nor is it inducible by retinoic acid. In N,N'-diphenyl-para-phenylenediamine-feeding experiments, it was shown that blocking epoxidation in vivo does not inhibit the function of retinoic acid. It is concluded that retinoic acid epoxidation is not required for retinoic acid function.