The role of fibrin fibrils in the dissociation of a cell surface protease-inhibitor complex and evidence for the recapture of the inhibitor protein.

Abstract

Colonic epithelial cells possess a cell surface protease referred to as guanidinobenzoatase (GB). Active GB can be located by the fluorescent active site directed competitive inhibitor 9-amino acridine (9AA) followed by fluorescence microscopy. The cell surface GB can be transferred to fibrin fibrils, which have a higher affinity for GB than the cell surface. The cytoplasm of colonic epithelial cells contains a protein which inhibits membrane bound GB, forming a latent form of GB or GB-inhibitor complex. This complex can also be dislodged from the epithelial cell surface due to the high affinity of fibrin for GB, with the consequent dissociation of the enzyme-inhibitor complex and solubilisation of the inhibitor. This use of fibrin has led to the demonstration of the transfer of a selective inhibitor protein from one cell surface (the donor) to a second cell surface (the target).