Testosterone Formation by Subcellular Particles of Rat Testes1

Abstract

Testicular tissue of normal adult rats was homogenized and fractionated by differential centrifugation. The microsomal fraction contained the most active enzymic systems for the cleavage of the side chain of 17α-hydroxyprogesterone-4-14C. Washed microsomes transformed progesterone-4-l4C, 17α-hydroxyprogesterone- 4-14C and Δ4-androstene- 3,17-dione-4-14C to testosterone-14C, indicating that the 17α-hydroxylase, the 17α-hydroxyprogesterone side chain cleavage enzyme and the 17β-hydroxysteroid dehydrogenase activities are all contained within the microsomes. NADPH was required for side chain cleavage of 17α-hydroxyprogesterone as well as for the convei-sion of androstenedione to testosterone by the rat testicular microsomes. Addition of the 105,000 × g supernatant fluid of the testicular homogenate to suspensions of testicular microsomes significantly increased the C,9 steroid formation from progesterone-4-14C and 17α-hydroxyprogesterone-4-14C. The stimulation was observed in the presence of excess NADPH or an NADPH-generating system. Long-term treatment of the microsomal suspension with sonic waves (10 kc) or addition of an anionic detergent to the suspension caused inactivation of the 17α-hydroxyprogesterone side chain cleavage enzyme. Neither washing the microsomes with hypertonic NaCl solution nor freezing and thawing the microsomal suspension released the enzyme activity from the microsomes. The results suggest that the enzyme is firmly combined with cytoplasmic particles. (Endocrinology76: 563, 1965)