Detection of intermediary Clr with complete active site, using a synthetic proteinase inhibitor

The synthetic proteinase inhibitor, FUT-175 (6-amidino-2-naphthyl-4-guanidinobenzoate), strongly suppressed activation of Clr at 37°C, causing 50% inhibition at 0.03 mM. To clarify whether the inhibitor was incorporated into the active site of intermediary Clr formed during the incubation, determination of the active site was tried using this inhibitor. Consequently, release of amidinonaphthol equimolar with the amount of Clr used was observed in the early period of incubation, in which the activation to Clr was about 5%. These results indicate that intermediary Clr already has a complete active site.