20α-HSD

20α-HSD belongs to the aldo-keto reductase superfamily. It relies on NADPH as a coenzyme and specifically reduces the C20 ketone group of progesterone to generate inactive 20α-hydroxyprogesterone. This enzyme is highly expressed in reproductive tissues including ovaries, corpus luteum, placenta and endometrium. Its core physiological function is to inactivate progesterone, thus regulating luteal homeostasis, menstrual cycles and labor initiation. It shows weak catalytic activity toward androgen substrates and differs significantly from 3α-HSD in substrate binding preference.