SOME CHARACTERISTICS OF 17-BETA-ESTRADIOL DEHYDROGENASE FROM BOVINE PLACENTA

The activity of 17β-estradiol dehydrogenase (E.C. 1.1.1.62) was measured, and its distribution in the subcellular fractions of bovine placenta was compared. Assay of activity was based on the formation of radioactive estrone from 17β[4-14C]-estradiol. Either NAD+ or NADP+ can serve as cofactor for the enzyme. The nuclear and microsomal fractions of the placental homogenate exhibited the highest specific enzymatic activities before and after treatment with Triton X-100. Electron micrographs of these two fractions prior to treatment with Triton X-100 showed satisfactory purity. 17β-estradiol dehydrogenase from bovine placenta exhibits a pH optimum of about 9.5-10.5, and is activated by 5 × 10-6M ZnC12; comparable concentrations of CaCl2 and MgCl2 inactivate the enzyme. The apparent Michaelis constants. Km, for 17β-estradiol and NAD+ are 1.4 × 1O-6M and 5.5 × 10-5M respectively. No 17α-estradiol dehydrogenase activity was demonstrable when using 17α-estradiol as substrate. © 1979.