Cystatin-SN (CST1)

Human saliva seems to include several cysteine proteinase inhibitors which are immunologically related to cystatin S but that differ in their specificity because of 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. .