Lb. Brattsten et al., IN-VITRO INHIBITION OF MIDGUT MICROSOMAL P450S FROM SPODOPTERA-ERIDANIA CATERPILLARS BY DEMETHYLATION INHIBITOR FUNGICIDES AND PLANT-GROWTHREGULATORS, Pesticide biochemistry and physiology, 48(3), 1994, pp. 234-243
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.