Ko te L-Cysteine tetahi o nga waikawa amino maori e 20, haunga te methionine, ko te mea anake kei roto he whanariki.He waikawa amino kore-matea kei roto i te thiol ka waikura hei hanga Cystine.He waikawa amino whanariki-kore i roto i te tangata, e pa ana ki te cystine, he mea nui a Cysteine mo te whakahiato pūmua, te whakakorenga, me nga mahi rerekee.Ka kitea i roto i te beta-keratin, te pūmua matua i roto i nga whao, kiri, me nga makawe, he mea nui te Cysteine i roto i te hanga collagen, me te kiri elasticity me te kakano.