Interaction between duodenase and Alpha₁-proteinase inhibitor

The interaction between duodenase, a newly recognized serine proteinase belonging to the small group of Janus-faced proteinases, and alpha₁-proteinase inhibitor (alpha₁-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 alpha₁-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 alpha₁-PI in identical compartments, alpha₁-PI is suggested to be a duodenase inhibitor in vivo.