Selenium in Thioredoxin Reductase: Resistance to Oxidative Inactivation, Oxidation States, and Reversibility of Chemical Reactions

This dissertation explored the role of selenium, specifically in the form of selenocysteine (Sec), in thioredoxin reductase (TrxR) and its resistance to oxidative inactivation. The study found that Sec's greater electrophilicity compared to cysteine (Cys) allows it to resist over oxidation, supporting the theory that Sec was selected for its ability to impart chemical reversibility to proteins. The research also questioned the effectiveness of dimedone in determining Sec's oxidation state, as it reacts with seleneninic and seleninic acids to form unstable adducts. Additionally, Sec-TrxR enzymes were shown to catalyze single electron reductions, likely due to a stable Sec radical intermediate.