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. Author manuscript; available in PMC: 2019 Nov 1.
Published in final edited form as: Free Radic Biol Med. 2018 Jun 5;127:215–227. doi: 10.1016/j.freeradbiomed.2018.06.002

Fig. 3. Bioactive Selenochemicals.

Fig. 3.

Se is present in biological systems in many forms, both inorganic and organic, with Se at different oxidation states (shown inside circles) and the chemicals present at different ionization states (charge given outside circle). Inorganic selenooxyanions (bottom), such as selenate, selenite, and selenium dioxide, are reduced to hydrogen selenide through the glutathione and thioredoxin systems. Selenide is present as HSe- at physiologic pH, converted to Se-phosphate and then to selenocysteine (Sec), existing mostly as the selenolate at physiologic pH. Sec is then incorporated into proteins (Sec-specific Proteins) via Sec-tRNA. Selenocysteine lysase rapidly converts Sec back to inorganic selenium quickly yielding selenide restarting the cycle. Selenomethionone (SeMet), a seleno-based nutrient absorbed from mammalian diets, can be incorporated into proteins in a non-specific manner (General Proteins), and can be converted to Sec or eliminated via conversion to dimethylselenide (DMSe). Hydrogen selenide also undergoes methylation to form either DMSe or trimethyl-selenide (TMSe) or can undergo conjugation with a sugar to be excreted from the biological system.