The interactions of protein inhibitors with tumour proteases studied in solution and immobilised on cell surfaces in frozen sections

The cell surface protease guanidinobenzoatase (GB) has been purified from human colonic and lung carcinoma tissue by an affinity step involving the binding of the enzyme either onto fibrin fibrils or onto agmatine-sepharose. The inhibitor protein (I) was extracted from the cytoplasm of tumour cells and isolated by an affinity step involving the binding of I to GB on the surface of cultured carcinoma cells. The interaction of GB and the I in solution was followed by kinetic studied employing the release of the fluorescent 4-methylumbelliferone (MU) from the synthetic substrate 4-methylumbelliferyl-p-guanidinozoate (MUGB)