ISOLATION OF CYSTEINE PROTEINASE-INHIBITOR, CYSTATIN-A, FROM HUMAN NAILS

A cysteine proteinase inhibitor was found in human nail extract treate d with 0.01 M Tris HCl buffer, pH 8.0. It had a 2-fold lower and a 4.5 -fold higher activity than that of human skin and hair extracts, respe ctively. From 5.9 g of human nail, 0.1 mg of cysteine proteinase inhib itor was obtained. It was purified by sequential DE-52 ion exchange an d carboxymethyl papain affinity chromotography. The purified inhibitor had an apparent molecular mass of 12 kDa as determined by sodium dode cyl sulphate polyacrylamide gel electrophoresis. It was more stable ag ainst heat and pH than most other proteins. Immunologically, it had th e same antigenicity compared with human epidermal cystatin A. Its N-te rminal amino acid sequence showed a mixed form comprising a full-lengt h MIPG sequence a truncated IPGG sequence. This sequence was identical to human cystatin A consisting of 20% of the full-length and 80% of t he truncated form. These results showed that human nail also contains cystatin A type cysteine proteinase inhibitor. Nails can be used as a source of cystatin A.