Demethylation of Methionine and Keratin Damage in Human Hair

The study examined the mechanism of homocysteine (Hcy) accumulation and keratin damage in human hair. It was found that Hcy-keratin levels increased 5–10-fold from the base to the tip of the hair, leading to a complete loss of keratin solubility in sodium dodecyl sulfate. This increase in Hcy-keratin was accompanied by a decrease in methionine-keratin and was correlated with hair copper and iron levels. In vitro experiments confirmed that Hcy generation from methionine depended on copper or iron, suggesting that copper/iron-catalyzed demethylation of methionine residues contributes to keratin damage in human hair.