Human saliva appears to contain several cysteine proteinase inhibitors that are immunologically related to cystatin S but that differ in their specificity due to amino acid sequence differences. Cystatin SN, with a pI of 7.5, is a much better inhibitor of papain and dipeptidyl peptidase I than is cystatin S, although both inhibit ficin equally well.
Subcellular locations: Secreted
Expressed in submandibular and sublingual saliva but not in parotid saliva (at protein level). Expressed in saliva, tears, urine and seminal fluid.