Mammalian 3‐Oxosteroid Δ⁵—Δ⁴‐Isomerase

Abstract

“Solubilization” of a beef adrenal microsomal enzyme: 3‐oxosteroid Δ 5 ‐Δ 4 ‐isomerase has been obtained by high concentrations of divalent cation (0.5–2 M CaCl 2 ). A study of the Solubilization yield as a function of ion concentration and pH has shown that optimum yield is obtained with 1 M CaCl 2 near pH 7. After elimination of calcium from the “soluble” enzyme, precipitation occurs and enzymatic activity is irreversibly lost in both precipitate and supernatant. The values of the kinetic parameters determined at pH 8.5 and 35°C are: V = 410 and 920 nmol · min −1 · mg −1 and K m = 36 and 11 μM for 5‐androstene‐3,17‐dione and 5‐pregnene‐3,20‐dione respectively. Our results suggest the existence of only one C 19 and C 21 3‐oxosteroid isomerase in the beef adrenal glands.