Interaction between Duodenase and α1-Proteinase Inhibitor

The interaction between duodenase, a newly recognized serine proteinase belonging to the small group of Janusfaced proteinases, and α1-proteinase inhibitor (α1-PI) from human serum was investigated. The stoichiometry of the inhibition was 1.2 mol/mol. The presence of a stable enzyme–inhibitor complex was shown by SDS-PAGE. The mechanism of interaction between duodenase and α1-PI was shown to be of the suicide type. The equilibrium and inhibition constants are 13 ± 3 nM and (1.9 ± 0.3)·105 M–1·sec–1, respectively. Based on the association rate constant of the enzyme–inhibitor complex and localization of duodenase and α1-PI in identical compartments, α1-PI is suggested to be a duodenase inhibitor in vivo.