Interaction between Human alpha₂-Macroglobulin and Duodenase, a Serine Proteinase with Dual Specificity

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O. O. Denisenko¹, T. S. Zamolodchikova², N. A. Popykina¹, and N. I. Larionova^1*

¹Department of Chemical Enzymology, Faculty of Chemistry, Lomonosov Moscow State University, 119992 Moscow, Russia; fax: (495) 939-5417; E-mail: natpopykina@mail.ru; nilar@enzyme.chem.msu.ru

²Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Miklukho-Maklaya 16/10, 117997 Moscow, Russia

^* To whom correspondence should be addressed.

Received October 25, 2005; Revision received December 15, 2005

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Interaction between a serine proteinase from bovine duodenum and human serum alpha₂-macroglobulin (alpha₂-MG) was studied. alpha₂-MG is established to be one of the most effective duodenase inhibitors. The enzyme is completely inhibited in less than 30 sec at equimolar ratio of the inhibitor and enzyme (concentration 2·10^-8 M). Under identical conditions, the rate of duodenase association with alpha₂-MG is at least 2.5-fold higher than the rate of chymotrypsin association with this inhibitor. The interaction with duodenase results in proteolysis of the inhibitor subunit in the “bait region”. Similarly to other proteases, duodenase in the complex with alpha₂-MG retains the intact catalytic apparatus and ability to hydrolyze some small substrates. But the duodenase-inhibitor complex is fully inactive to proteins (bovine serum albumin). The stoichiometry of the enzyme interaction with the inhibitor is 2 : 1 (mol/mol). Based on the association rate constant and the termination time of the duodenase and alpha₂-MG in vivo association, alpha₂-MG is suggested to be a physiological regulator of the enzyme.

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KEY WORDS: duodenase, alpha₂-macroglobulin, inhibition, stoichiometry, kinetics

DOI: 10.1134/S0006297906060101

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