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Interaction between human alpha2-macroglobulin and duodenase, a serine proteinase with dual specificity
O O Denisenko1, T S Zamolodchikova, N A Popykina
1Department of Chemical Enzymology, Faculty of Chemistry, Lomonosov Moscow State University, Moscow, 119992, Russia. nilar@enzyme.chem.msu.ru.
Abstract:
Interaction between a serine proteinase from bovine duodenum and human serum alpha(2)-macroglobulin (alpha(2)-MG) was studied. alpha(2)-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 x 10(-8) M). Under identical conditions, the rate of duodenase association with alpha(2)-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 alpha(2)-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 alpha(2)-MG in vivo association, alpha(2)-MG is suggested to be a physiological regulator of the enzyme.
Insights
Human serum alpha(2)-macroglobulin (alpha(2)-MG) effectively inhibits bovine duodenase, a serine proteinase. This interaction suggests alpha(2)-MG acts as a physiological regulator for duodenase activity in vivo.
Area of Science:
- Biochemistry
- Enzymology
- Protease Inhibitors
Background:
- Human serum alpha(2)-macroglobulin (alpha(2)-MG) is a major plasma protease inhibitor.
- Bovine duodenase is a serine proteinase found in the duodenum.
- Understanding protease-inhibitor interactions is crucial for physiological regulation.
Purpose of the Study:
- To investigate the interaction between bovine duodenase and human alpha(2)-macroglobulin.
- To determine the inhibitory kinetics and stoichiometry of this interaction.
- To evaluate the potential physiological role of alpha(2)-MG in regulating duodenase activity.
Main Methods:
- Enzyme inhibition assays were performed at equimolar concentrations (2 x 10(-8) M).
- Association rates of duodenase and chymotrypsin with alpha(2)-MG were compared.
- Proteolysis of the alpha(2)-MG subunit and substrate hydrolysis by the complex were analyzed.
- Stoichiometry of the enzyme-inhibitor complex was determined.
Main Results:
- alpha(2)-MG completely inhibited duodenase within 30 seconds at equimolar ratios.
- Duodenase associated with alpha(2)-MG at least 2.5-fold faster than chymotrypsin.
- Duodenase proteolyzed the alpha(2)-MG bait region, forming a 2:1 (enzyme:inhibitor) complex.
- The duodenase-alpha(2)-MG complex retained catalytic activity towards small substrates but not proteins.
Conclusions:
- alpha(2)-MG is a potent inhibitor of bovine duodenase.
- The rapid association rate and stoichiometry suggest alpha(2)-MG functions as a physiological regulator of duodenase in vivo.
- The interaction involves specific proteolysis of alpha(2)-MG by duodenase.
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