REDUCTION OF 11-OXY AND 11-DEOXY STEROIDS BY MAMMALIAN LIVER Δ4-HYDROGENASES

Abstract

SUMMARY 1. The steroid Δ4-hydrogenases occurring in liver of both sexes of rats, mice, hamsters, rabbits and guinea-pigs have been investigated in vitro. 2. In both sexes of the species studied, with the exception of the female rat, Δ4-hydrogenase activity was found to be present in both the microsomal and 105,000 g supernatant fractions. 3. The reactivity of these enzyme preparations has been studied with a variety of 11-deoxy, 11β-hydroxy and 11-keto compounds. In general, the enzyme preparations (microsomal and soluble) of guinea-pig, mouse and rabbit liver reduced the 11β-hydroxy compounds to a lesser degree than the 11-deoxy and 11-keto analogues. A similar pattern of reactivity was exhibited by the soluble enzyme preparations of livers from the male rat and hamster. But the microsomal preparations of these two species, in contrast to the other preparations studied, reduced the 11β-hydroxy compounds almost as readily as the 11-keto and 11-deoxy compounds. 4. It is concluded that the differences observed in the relative rates of Δ4 reduction of 11β-hydroxy compounds as compared with 11-keto and 11-deoxy compounds are consistent with some degree of enzyme group specificity. 5. The relationship between the observations in vitro and the urinary steroid excretion pattern is discussed.