The disulphide bridges of human cystatin C (γ-trace) and chicken cystatin

AbstractHuman cystatin C, a powerful physiological protein inhibitor of cathepsins B, H and L, contains two disulphide bridges, at least one of which is essential to its inhibitory activity. The positions of these bridges in the single polypeptide chain of the protein have been determined by diagonal paper electrophoresis. The cysteine residues at positions 73 and 83 form one bridge, and those at positions 97 and 117 form the other. In the homologous cystatin of chicken egg-white, the disulphides are Cys 71–Cys 81, and Cys 95–Cys 115