Cysteine proteinase inhibitors in human squamous cell carcinoma

Cysteine proteinase inhibitors in Tris extract of human skin squamous cell carcinoma tissue were studied. From 17.2g of the tissue, approximately equal to 113.5 U inhibitor was obtained. With Sephadex G-75 gel chromatography, 3 papain inhibitor peaks of Mr approximately equal to 100,000, 38,000, and 12,000 were separated. In the immunodiffusion studies, Mr approximately equal to 100,000 fractions reacted with antisera made against human kininogen (alpha-cysteine proteinase inhibitor) and cystatin B. By using alkali treatment, free cystatin B was dissociated from the Mr approximately equal to 100,000 fractions. It is suggested that Mr approximately equal to 100,000 fractions contain cystatin B and alpha-cysteine proteinase inhibitor complexed with tissue proteinases. The Mr approximately equal to 38,000 fractions reacted with antiserum made against the papain inhibitor of Mr approximately equal to 43,000. The inhibitors in the Mr approximately equal to 12,000 fractions were identified as cystatin A and B on the basis of their reactions with antisera made against these inhibitors purified from human tissues.