Estradiol sulfate
Although inactive at steroid hormone receptors , E2S has been found to act as a potent inhibitor of glutathione S-transferase , an enzyme that contributes to the inactivation of estradiol via conversion of it into an estradiol-glutathione conjugate . As such , E2S can indirectly serve as a positive effector of estrogen signaling . 
<triplet> inhibitor <subj> enzyme <obj> physically interacts with