The branched pathway of a suicide substrate mechanism. The inhibitor (I) forms a reversible complex (EI) with its target serine protease (E), characterized by the bimolecular rate constant k1 and the dissociation rate constant k−1 . Subsequently, an intermediate complex (EI′) is formed, which can convert with a rate constant k4 into the SDS-stable complex E-I# or it can react according to a substrate mechanism, resulting in free enzyme and cleaved inhibitor (I*) with the corresponding rate constant k3 . The partition ratio (r = k3/k4 ) represents the number of catalytic turnovers per inactivation event, 1 + r is the apparent stoichiometry. Finally, the stable bimolecular complex (E-I#) can dissociate with a rate constant k5 into the free active enzyme (E) and cleaved, inactive inhibitor (I*).
