IN-VITRO INHIBITION OF MIDGUT MICROSOMAL P450S FROM SPODOPTERA-ERIDANIA CATERPILLARS BY DEMETHYLATION INHIBITOR FUNGICIDES AND PLANT-GROWTHREGULATORS

The demethylation inhibitor fungicides diniconazole, propiconazole, an d triadimefon, and the plant growth regulators uniconazole and pachlob utrazole inhibit microsomal cytochrome P450s from midguts of Spodopter a eridania sixth-instar caterpillars. The I-50 values for O-demethylat ion of methoxyresorufin in microsomes from caterpillars fed a diet con taining 0.2% pentamethylbenzene (PMB) for 3 days ranged from 0.3 to 13 0 mu M, For N-demethylation of p-chloro-N-methylaniline in microsomes from caterpillars fed a control diet, i.e., without inducer, the I(50) s were from 33 to 857 mu M. There were no consistent differences in in hibitory efficacy between fungicides and plant growth regulators. The induced isozyme(s) catalyzing the O-demethylation was more sensitive t han the constitutive isozyme(s) catalyzing N-demethylation to inhibiti on by the compounds. Inhibition of both activities was mixed, indicati ng the presence of more than one isozyme catalyzing each reaction. Bot h substrates and all inhibitors used formed complexes with oxidized mi crosomes and caused type 2 spectral perturbations. Sodium dodecyl sulf ate-polyacrylamide gel electrophoresis and immunoblotting with an anti body to a Drosophila melanogaster P450 isozyme of microsomes from cont rol and induced S. eridania also indicate the presence of several P450 isozymes; at least three, which may be P450s, were induced. Two of th e control isozymes and three of the isozymes in microsomes from PMB-fe d caterpillars cross-reacted strongly with the antibody. (C) 1994 Acad emic Press, Inc.