Interaction between duodenase and alpha(1)-proteinase inhibitor

The interaction between duodenase, a newly recognized serine proteinase bel onging to the small group of Janus-faced proteinases, and alpha (1)-protein ase inhibitor (alpha (1)-PI) from human serum was investigated. The stoichi ometry of the inhibition was 1.2 mol/mol. The presence of a stable enzyme-i nhibitor complex was shown by SDS-PAGE. The mechanism of interaction betwee n duodenase and alpha (1)-PI was shown to be of the suicide type. The equil ibrium and inhibition constants are 13 +/- 3 nM and (1.9 +/- 0.3) . 10(5) M (-1 .)sec(-1), respectively. Based on the association rate constant of the enzyme-inhibitor complex and localization of duodenase and alpha (1)-PI in identical compartments, alpha (1)-PI is suggested to be a duodenase inhibit or in vivo.