Intracellular distribution and substrate specificity of steroid 11 -hydroxylase in testes of rainbow trout (Salmo gairdneri).

Abstract

Subcellular fractions of testes of rainbow trout (Salmo gairdneri) were prepared by a differential centrifugation, examined under an electron microscope, and incubated with 4-14C-labeled androstenedione, testosterone, 11-deoxycorticosterone, or 11-deoxycortisol at 16°C for 60 min under an aerobic condition. After identification of the metabolites obtained, activities of 11β-hydroxylase, 17α-hydroxylase, and 17β-hydroxysteroid dehydrogenase per unit weight of protein were estimated from the quantities of the metabolites. Among the subcellular fractions, the activity of 11β-hydroxylase upon testosterone, 11-deoxycorticosterone, and 11-deoxycortisol was found concentrated in the mitochondrial fraction, while the activities of 17α-hydroxylase upon 11-deoxycorticosterone and 17β-hydroxysteroid dehydrogenase upon androstenedione and testosterone were localized mostly in the microsomal fraction. Moreover, the 11β-hydroxylase in the rainbow trout testes preferred 11-deoxycorticosterone most and 11-deoxycortisol next as the substrate, whereas testosterone was hydroxylated at 11β-position in low yield and androstenedione was not. By raising incubation temperature from 16°C to 37°C, 11β-hydroxylation of testosterone was not enhanced at all, while the 17β-hydroxysteroid dehydrogenase activity was increased more than two times as much as the activity at 16°C. From the results obtained, the biosynthetic pathway of 11-oxygenated androgens in the teleostean testes were discussed.