Oxidation of steroids with the 20β-hydroxy-21-oxo side chain to 20β-hydroxy-21-oic acids by horse liver aldehyde dehydrogenases

Abstract

In this paper we show that C₂₁ steroids with the 20β-hydroxy-21-aldehyde side chain (isocorticosteroids) are oxidized by horse liver aldehyde dehydrogenases to 20β-hydroxy-21-oic acids. The aldehyde de-hydrogenases F1 and F2, purified as described by Eckfeldt et al. [10] had different substrate specificities. Isoenzyme F1 oxidized 17α-hydroxylated steroids; isoenzyme F2 oxidized 17-deoxysteroids. Steroids with the 20-oxo-21-aldehyde side chain were poor substrates. With isoenzymes F1 and F2, enzyme activity increased between pH 6 and 9.5 with no optimum. The K_M values of the F1 enzyme for isocortisol was 3 × 10⁻⁵ M and of F2 for isoDOC was 9 × 10⁻⁵M with NAD⁺ as cofactor. Low concentrations of methanol, ethanol and isopropanol inhibited the oxidations. The acids resulting from the oxidation of 11β,17,20β-trihydroxy-3-oxo-4-[l,2-³H]-pregnen-21-al and 20β-hydroxy-3-oxo-4-[4-¹⁴C]-pregnene 21-al were isolated and identified. The results support our postulate that the oxidation of corticosteroids to 20-hydroxy-21-oic acids may proceed through 20-hydroxy-21-aldehyde intermediates.