Isolation of cysteine proteinase inhibitor, cystatin A, from human nails.

A cysteine proteinase inhibitor was found in human nail extract treated 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, respectively. From 5.9 g of human nail, 0.1 mg of cysteine proteinase inhibitor was obtained. It was purified by sequential DE-52 ion exchange and carboxymethyl papain affinity chromatography. The purified inhibitor had an apparent molecular mass of 12 kDa as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis. It was more stable against heat and pH than most other proteins. Immunologically, it had the same antigenicity compared with human epidermal cystatin A. Its N-terminal amino acid sequence showed a mixed form comprising a full-length MIPG sequence a truncated IPGG sequence. This sequence was identical to human cystatin A consisting of 20% of the full-length and 80% of the 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.