Human cysteine proteinases and their protein inhibitors stefins, cystatins and kininogens

The cathepsins B, H and L of human origin were isolated in pure form in sufficient quantities for structural characterization. The complete amino acid sequence of human liver cathepsin B was determined. Partial amino acid sequences of the human kidney cathepsin H and L show the highly conserved region around the active site cysteine. The cysteine proteinase inhibitors stefin A, human stefin B and human cystatin C were isolated, characterized and sequenced. Their amino acid sequences are compared with sequences of other protein inhibitors of the stefin and cystatin family, showing a high degree of homology throughout both families. The stefin and cystatin family, together with newly discovered kininogen family belong to the same superfamily of cystatins. The constructed dendrogram shows that the most closely related inhibitors so far sequenced are human stefin B and rat liver TPI.