METABOLISM AND MECHANISM OF ACTION OF OESTROGENS .12. STRUCTURE AND MECHANISM OF FORMATION OF WATER-SOLUBLE AND PROTEIN-BOUND METABOLITES OF OESTRONE IN RAT-LIVER MICROSOMES IN VITRO AND IN VIVO

1. 1. During aerobic incubation of labeled oestrone or 2-hydroxyoestrone with rat-liver microsomes and NADPH, the steroid is bound to supernatant factors, e.g. glutathione and cysteine, and to microsomal proteins. Glutathione and protein compete for the same steroid metabolite. 2. 2. The binding reaction shows a remarkable specificity for sulfhydryl compounds; amino compounds are not bound. As far as the thiol is concerned, the binding reaction is nonspecific. A comparison of the properties of the metabolites, obtained by trapping the radioactivity with different thiols, demonstrates the formation of a thioether linkage. 3. 3. In carrier experiments with α-hydroxy-[4-14C]oestrone as substrate and with thioglycolic acid as trapping agent, mainly 2-hydroxy-4-carboxymethylmercapto-oestrone is formed. An o-quinone being excluded, these results suggest that the oestrogen metabolite bound by thiols is an o-semiquinone of 2-hydroxyoestrone. 4. 4. After injection of physiological doses of [6,7-3H2]oestrone, a long-lasting covalent protein binding can be demonstrated in rat liver in vivo. This reaction occurs especially in the microsomal fraction. 5. 5. The physiological significance of the binding reaction is discussed. © 1969.