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

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/O-2 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 O-2 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/O-2 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. (C) 2000 Elsevier Science B.V. All rights reserved.