Aldose and aldehyde reductase exhibit isocorticosteroid reductase activity

In this paper we describe the reduction of corticosteroid metabolites containing the 17 beta-aldol side chain (isocorticosteroids) by aldose and aldehyde reductase from human tissues. Aldose reductase catalyzed the reduction of the aldehydes derived from cortisol and corticosterone at about the same rate, whereas aldehyde reductase preferentially acted on the aldehydes derived from 17-deoxycorticosteroids. At comparable rates of reduction the Michaelis constants for the best steroid aldehydes were one order of magnitude lower than for the hitherto best substrates. We propose that aldose and aldehyde reductase participate in the conversion of the corticosteroid ketol side chain to the glycol side chain via an aldol intermediate by the 'long loop' pathway proposed by Monder and Bradlow [(1977) J. Steroid Biochem. 8, 897-908].