Selenium Methylation: Insights into Chemical Reactions and Enzymatic Pathways

Selenium, an essential metalloid, plays a dual role in biological systems: while crucial for various physiological functions, its excess can lead to toxicity. Organisms mitigate selenium toxicity through a biochemical process known as methylation, which transforms inorganic selenium species into less harmful organic forms. This review was conducted through a targeted search of multiple databases, including PubMed, Scopus, Web of Science, and Google Scholar. Keywords such as "selenium methylation", "selenium chemical reactions", “detoxification’ “methylation mechanisms and pathways” and “enzymatic processes”, were used to gather a broad and relevant selection of articles. This article provides a comprehensive examination of the mechanisms, pathways, and enzymatic processes involved in selenium methylation, with a focus on both chemical reactions and environmental impacts. Selenium methylation involves converting inorganic selenium forms like selenite and selenate, into less toxic organic compounds, such as monomethylselenide (MMSe) and dimethylselenide (DMSe) through intermediates like hydrogen selenide. Various enzymes, including glutathione reductase and S-adenosylmethionine (SAM)-dependent methyltransferases catalyze critical steps, such as reducing selenite to hydrogen selenide and methylating it to form MMSe and DMSe. The review also explores the role of selenocysteine lyase in processing organic selenium and factors affecting the efficiency of these processes, including environmental conditions. In conclusion, this paper explores selenium methylation in plants, focusing on rice and corn, and how their selenium uptake and metabolism are affected by environmental factors. It examines the conversion of selenium into organic forms like selenomethionine and selenocysteine, and the role of methylation in managing excess selenium. The findings offer insights into selenium chemistry, with implications for food safety, nutrition, and environmental management, addressing key knowledge gaps and enhancing our understanding of selenium’s biological and chemical roles.