Evidence of Direct Conversion of Testosterone Sulfate to Estradiol 17-Sulfate by Human Placental Microsomes

Abstract

Ring A aromatization of testosterone sulfate (TS), using human term placental microsomes as a enzyme source, was examined under a reduced nicotinamide adenine dinucleotide phosphate (NADPH)-generating system. The aromatization to estradiol 17-sulfate (ES) without removal of the C-17 conjugate group was confirmed. Judging from the results of various experiments, including an inhibition experiment, the conversion was considered to occur by placental aromatase. Apparent K_m and V_max values for this aromatization were determined to be 37.4 μM and 330 pmol/mg protein/min respectively. The physiological role of direct conversion of TS by placenta to ES is discussed in connection with pregnancy.