The molecule is a cysteine zwitterion derived from D-cysteine by transfer of a proton from each of the carboxy groups to the amino groups. It is an enantiomer of a L-cystine zwitterion. It is a tautomer of a D-cystine.
(2S)-2-azaniumyl-3-[[(2S)-2-azaniumyl-2-carboxylatoethyl]disulfanyl]propanoate