Human estrogenic 17beta-hydroxysteroid dehydrogenase: predominance of estrone reduction and its induction by NADPH.
Human estrogenic 17beta-hydroxysteroid dehydrogenase (17beta-HSD1) plays a crucial role in the last step of the synthesis of estrogens. A detailed kinetic study demonstrated that the enzyme shows about 240 fold higher specificity towards estrone reduction than estradiol oxidation at physiological pH using tri-phosphate cofactors. The kcat/Km values are 96 +/- 10 and 0.4 +/- 0.1 s-1 (microM)-1 respectively for the above two reactions. However, it has been shown that this difference is closely linked to the use of NADPH and NADP cofactors. A binding study using equilibrium dialysis indicated similar KD (equilibrium dissociation constant) of 11 +/- 1 and 4.7 +/- 0.9 microM for estrone and estradiol, respectively. The binding affinity of 17beta-HSD1 to estrone was significantly increased with a KD of 1.6 +/- 0.2 microM in the presence of NADP, the latter used as an analogue of the NADPH. The results of binding studies agree with the steady-state kinetics, which showed that the Km of estrone is 12-fold lower when using NADPH as a cofactor than when using NADH. These results strongly suggest that the cofactor plays a crucial role in the stimulation of the specificity for estrogen reduction.
Jin
J Z
JZ
CHUL Research Center, Laval University, Quebec, Quebec, G1V 4G2, Canada.
Lin
S X
SX
D015067:17-Hydroxysteroid Dehydrogenases / Q000096:biosynthesis*; D001665:Binding Sites; D004790:Enzyme Induction / Q000187:drug effects; D004958:Estradiol / Q000378:metabolism; D004970:Estrone / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009243:NAD / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010920:Placenta / Q000201:enzymology; D011485:Protein Binding
D009243:NAD; D004970:Estrone; D004958:Estradiol; D009249:NADP; D015067:17-Hydroxysteroid Dehydrogenases; C044256:3 (or 17)-beta-hydroxysteroid dehydrogenase