Chorion peroxidase-mediated NADH/O2 oxidoreduction cooperated by chorion malate dehydrogenase-catalyzed NADH production: a feasible pathway leading to H2O2 formation during chorion hardening in Aedes aegypti mosquitoes

摘要

A specific chorion peroxidase is present in Aedes aegypti and this enzyme is responsible for catalyzing chorion protein cross-linking through dityrosine formation during chorion hardening. Peroxidase-mediated dityrosine cross-linking requires H2O2, and this study discusses the possible involvement of the chorion peroxidase in H2O2 formation by mediating NADH/O2 oxidoreduction during chorion hardening in A. aegypti eggs. Our data show that mosquito chorion peroxidase is able to catalyze pH-dependent NADH oxidation, which is enhanced in the presence of Mn²⁺. Molecular oxygen is the electron acceptor during peroxidase-catalyzed NADH oxidation, and reduction of O2 leads to the production of H2O2, demonstrated by the formation of dityrosine in a NADH/peroxidase reaction mixture following addition of tyrosine. An oxidoreductase capable of catalyzing malate/NAD⁺ oxidoreduction is also present in the egg chorion of A. aegypti. The cooperative roles of chorion malate/NAD⁺ oxidoreductase and chorion peroxidase on generating H2O2 with NAD⁺ and malate as initial substrates were demonstrated by the production of dityrosine after addition of tyrosine to a reaction mixture containing NAD⁺ and malate in the presence of both malate dehydrogenase fractions and purified chorion peroxidase. Data suggest that chorion peroxidase-mediated NADH/O2 oxidoreduction may contribute to the formation of the H2O2 required for chorion protein cross-linking mediated by the same peroxidase, and that the chorion associated malate dehydrogenase may be responsible for the supply of NADH for the H2O2 production.