The covalent acylation of the dasTMPRSS2 active site with nafamostat and other ester inhibitors was measured using reaction progress curve fitting that has been described for dasTMPRSS11D . Briefly, stocks of Boc-QAR-AMC substrate pre-mixed with various concentrations of nafamostat (or other ester compounds) were transferred to wells containing dasTMPRSS2 enzyme and fluorescence immediately read to capture the production of AMC dye and rapid arrest of dasTMPRSS2 activity by the inhibitor.