Cysteine Assay Kit (Visible Spectrophotometry)

Proteins contain three sulfur-containing amino acids: methionine, cystine, and cysteine (Cys). Among them, Cys is the only sulfur-containing amino acid with a sulfhydryl group. It is derived from methionine and can interconvert with cystine. Cys participates in the formation of disulfide bonds in proteins, often serving as a component of the active site, and provides sulfhydryl groups for other physiological and biochemical reactions. Additionally, Cys accumulates extensively on the skin and mucosal surfaces, maintaining the activity of important sulfhydryl enzymes in keratin production and replenishing sulfhydryl groups to support normal skin metabolism. It also regulates the production of basal melanin by pigment cells in the innermost layer of the epidermis, contributing to effects such as skin whitening, detoxification, and improvement of inflammatory and allergic skin conditions.