modified L-cysteine residue L-cystine -2.0156500339508056641 -2.0199999809265136719 This modification occurs naturally in two forms. It exists as a disulfide cross-link of two cysteine residues (MOD:00034), or as a disulfide cross-link of a cysteine residues and a free cysteine (MOD:00765). 2-amino-3-(2-amino-2-carboxy-ethyl)disulfanyl-propanoic acid bis(alpha-aminopropionic acid)-beta-disulfide dicysteine 3,3'-dithiobis(2-aminopropanoic acid) beta,beta'-dithiodialanine 3,3'-dithiobisalanine PSI-MOD none A protein modification that forms L-cystine by forming a disulfide bond that either cross-links two peptidyl L-cysteine residues, or modifies a peptidyl cysteine with a free cysteine. beta,beta'-diamino-beta,beta'-dicarboxydiethyldisulfide Cystine ((Cys)2) bis(beta-amino-beta-carboxyethyl)disulfide L-cystine Cys2 MOD:01626 3,3'-disulfane-1,2-diylbis(2-azanylpropanoic acid) 3,3'-dithiodialanine none H -2 none natural (2R,2'R)-3,3'-disulfane-1,2-diylbis(2-aminopropanoic acid)