Use of p-aminobenzamidine to monitor activation of trypsin-like serine proteases.

The fluorescent compound p-aminobenzamidine was used to monitor activation of the trypsin-like serine proteases trypsin, thrombin, and blood coagulation factors IXa and Xa. p-Aminobenzamidine, when bound to the activated forms of these proteases but not the corresponding zymogens, displayed an increase in fluorescence. This fluorescence increase was coincident with activation as measured by synthetic substrate hydrolysis, physiological coagulation activity, and the appearance of activation products on gel electrophoresis. The activation of proteolytically modified factor X was also monitored. These results suggest that following p-aminobenzamidine fluorescence is a convenient procedure for monitoring activation of trypsin-like serine proteases.