Carbonyl reductase activity of a pluripotent enzyme, 3α-hydroxysteroid dehydrogenase from Pseudomonas sp. B-0831

We found that 3α-hydroxysteroid dehydrogenase (3α-HSD) from Pseudomonas sp. B-0831 can catalyze the carbonyl reduction of non-steroid substrates, such as metyrapone and p-nitrobenzaldehyde, in addition to the activity of 3α-hydroxysteroid dehydrogenase. The results of an inhibition study in metyrapone reduction by androsterone and cholic acid indicated that metyrapone bound to the same catalytic site as the steroids. The Km values for the carbonyl reduction were relatively higher than those for the oxidoreduction at position 3 of the steroid nucleus. It should be noted that the kcat value of metyrapone using NADPH as a cofactor was less than 1% of that with NADH, indicating that the cofactor binding modulates the catalytic activity. The present result clearly showed that 3α-HSD from P. sp. B-0831 has pluripotent substrate specificity and can be named 3α-hydroxysteroid dehydrogenase/carbonyl reductase (3α-HSD/CR).