Figure 1. Biotin-RQRR-CMK efficiently inhibits matriptase even after 3 hours of pre-incubation at 37°C.

(A) Schematic structure of the biotin-RQRR-CMK peptide inhibitor. (B) The reactivity of biotin-RQRR-CMK was tested after 180 min of pre-incubation at 37°C (diamonds) or without preincubation (crosses). 0.2 µM matriptase SPD was incubated for 10 min at 37°C with (diamonds and crosses) or without (squares) 50 µM biotin-RQRR-CMK before addition of the chromogenic substrate to a final concentration of 300 µM. (C) The stability of 5 nM biotin-RQRR-CMK was further tested after the time points 0 (crosses), 60 (circles), 120 (stars), and 180 min (diamonds) of pre-incubation at 37°C and compared to a control not containing biotin-RQRR-CMK (squares). As described above, 0.2 nM matriptase SPD was added to each sample and incubated for 10 min at 37°C followed by addition of the chromogenic substrate to a final concentration of 300 µM. In all cases, the enzymatic activity of SPD was monitored by conversion of the chromogenic substrate (S2288). Each plot shows the change in optical density at 405 nm of the reaction mixture as a function of reaction time. The presence of active protease results in a continued release of a yellow cleavage product resulting in a linear color development in agreement with a pseudo 1^st order reaction due to the high molar excess of substrate to protease. Results shown are representative of 3 independent experiments.