L-Cysteine ndi imodzi mwa ma amino acid 20 achilengedwe ndipo, pambali pa methionine, ndi imodzi yokha yomwe ili ndi sulfure.Ndi thiol yokhala ndi amino acid osafunikira omwe amapangidwa ndi okosijeni kuti apange Cystine.Ndiwosafunikira sulfure wokhala ndi amino acid mwa anthu, wokhudzana ndi cystine, Cysteine ndiwofunikira pakupanga mapuloteni, kuchotsa poizoni, ndi ntchito zosiyanasiyana za metabolic.Cysteine imapezeka mu beta-keratin, puloteni yayikulu mu misomali, khungu, tsitsi, ndi tsitsi, cysteine ndi yofunika kwambiri pakupanga kolajeni, komanso kusungunuka kwa khungu ndi mawonekedwe.