Properties of NADPH-dependent carbonyl reductases in rat liver cytosol

Rat liver cytosol was shown previously by us to contain multiple forms of 3 alpha-hydroxysteroid dehydrogenase. Two (F4-II and -III) of the seven forms were purified to homogeneity, and four (F3-II, -III, -IV and F4-I) of them partially purified. One of them (F4-III) has been shown previously to catalyze the reduction of long-chain aliphatic and aromatic aldehydes or aromatic ketones as well as 3-oxosteroids [M. Ikeda et al., Biochem. Pharmac. 30, 1931 (1981)]. The reducing activity of such compounds was examined with the other F4 enzymes, and it was revealed that they also reduce a number of carbonyl compounds described above. In addition, quinones were tested for the first time in this report as substrates for all the F4 enzymes, and among them 9,10-phenanthrenequinone was found to be the best substrate for them, followed by hydrindantin and 2,6-dichlorophenolindophenol, while menadione was a poor substrate. The F4 enzymes did not catalyze the reduction of the oxo group at the 9-position of the prostaglandins of the E and A class with NADPH or NADH. On the basis of this evidence, the identity of ketone reductases (F4-I-III) in the rat liver is proposed to be 3 alpha-hydroxysteroid dehydrogenase, rather than prostaglandin 9-ketoreductase, which was demonstrated to correspond to ketone reductase in human brain [B. Wermuth, J. biol. Chem. 256, 1206 (1981)].