Studies on 17beta-hydroxysteroid dehydrogenase in human endometrium and endometrial carcinoma

Kinetic parameters, substrate specificity and stability of a cytoplasmic 17beta-hydroxysteroid dehydrogenase of human secretory endometrium were studied. Using oestradiol as substrate, oestrone formation was found to be linear with time and the concentration of protein. The optimum temperature was 40 degrees C and the optimum pH 9.5. For the reduction of oestrone the optimal pH was 6. With NADP the maximal velocity was about 1/3 of that with NAD (0.23 nmoles/mg protein/10 min). The Km for oestradiol was 3.3 times 10- minus 6 M. Testosterone and androstenedione also served as substrates but they were interconverted more slowly than oestradiol and oestrone. Sulphhydryl groups were shown to be essential for catalysis. The enzyme is cold sensitive but cold inactivation can be reduced by NAD, NADP, oestradiol or glycerol.