Mouse anti-L-Cysteine monoclonal antibody for WB, IHC, IF, IP, ELISA. Cysteine (abbreviated as Cys or C) is an alpha-amino acid with the chemical formula HO2CCH(NH2)CH2SH. It is a semi-essential amino acid, which means that it can be biosynthesized in humans. Its codons are UGU and UGC. Cysteine was considered to be a hydrophilic amino acid based on the belief that the thiol group interacts well with water. However, the cysteine side chain participates in the hydrophobic bonding system of the micelle. The quantitative comparison of the values of the critical micelle concentrations leads to the conclusion that the CH2SH group of amino acid has the same effect on the micelle stability as a methylene group of the hydrocarbon tail. Therefore, there is justification for the recently voiced assumptions of the hydrophobic nature of the cysteine side chain in proteins. The thiol side chain often participates in enzymatic reactions, serving as a nucleophile. The thiol is susceptible to oxidization to give the disulfide derivative cystine, which serves an important structural role in many proteins. When used as a food additive, it has the E-number E920.