Aldehyde reductase from rat liver is a 3 alpha-hydroxysteroid dehydrogenase.

Rat liver was previously shown to contain [V.G. Erwin and R.A. Deitrich, Biochem. Pharmacol.21, 2915 (1972)] two aldehyde reductases (EC 1.1.1.2) in addition to alcohol dehydrogenase (EC 1.1.1.1). The present paper demonstrates that one of these aldehyde reductases also catalyzes reversible reduction of 3-ketosteroids of A/B cis configuration. The product of reduction appears to be 3α-alcohol, rather than 3β-alcohol, the product of reduction of the same 3-ketone by rat liver alcohol dehydrogenase. This difference in the steric course of reduction may be useful for distinguishing aldehyde reductase from alcohol dehydrogenase. Since 3α-alcohols of A/B cis configuration are universally distributed in the bile of vertebrates, the steroid activity of aldehyde reductase may be connected with its physiological function.