[Binding of FITC-labelled alpha-thrombin by peritoneal mast cells]

The interaction of bovine alpha-thrombin with peritoneal mast cells was studied using FITC-labeled enzyme. Thrombin was modified with FITC in the presence of heparin and was separated from heparin and free FITC by gel-filtration at HPLC yielding FITC-labeled alpha-thrombin with intact additional recognition binding site for high molecular substrates and cell receptors. Equilibrium studies have shown that the binding of thrombin to peritoneal mast cells is active independent, rapid, specific, saturable and reversible. Equilibrium between bound and free thrombin is attained within I min and Scatchard analysis indicates a population of approximately 54 x 10(3) sites/cell with a dissociation constant of 1.3 x 10(-9) M. FITC-labeled alpha-thrombin binds to peritoneal mast cells in a temperature-dependent manner with optimum at 37 degrees C. These results indicate that FITC-labeled alpha-thrombin binds to peritoneal mast cells with high affinity.