PARTIAL CHARACTERIZATION OF MICROSOMES ISOLATED FROM MUNG BEAN COTYLEDONS

Microsomes isolated from excised cotyledons of 3-day-old, dark-grown, mung bean (Vigna radiata, L., cv Berken) seedlings metabolized two end ogenous substrates (cinnamic acid and lauric acid), three organophosph ate insecticides (diazinon, isazofos, and methidathion), three acetami de herbicides (metolachlor, CGA-24704, and alachlor), and bentazon. Ci nnamic acid was aryl hydroxylated forming p-coumaric acid. Lauric acid was primarily hydroxylated at the terminal carbon (omega-hydroxylatio n). The three alpha-chloroacetamides were O-demethylated. With all thr ee organophosphate insecticides, the phosphorothionate sulfur was oxid ized to the corresponding oxon and the phosphoroester oxygen was cleav ed in both diazinon and isazofos. Bentazon was aryl hydroxylated formi ng the 6-hydroxy derivative. The concentration of cytochrome P450 in t he microsomal preparations was marginally enhanced by pretreatment of the seed with naphthalic anhydride (NA), but was markedly increased by subirrigation of NA-treated seed with ethanol and was additionally in creased with the combination of NA, clofibrate, and ethanol. The exten t of metabolism of only lauric acid paralleled the increases in cytoch rome P450 content. The various seed/seedling treatments, however, did approximately double the rate of metabolism of the three organophospha tes, the three chloroacetamides, and bentazon. Metabolism required a r educed pyridine nucleotide and was affected by several cytochrome P450 monooxygenase inhibitors (carbon monoxide, tetcyclacis, piperonyl but oxide, 1-aminobenzotriazole, and SKF-525A). The inhibitors differentia lly affected metabolism of the substrates. Microsomal oxidations from both untreated and inducer-treated tissue responded similarly to the i nhibitors. The differential inhibitory responses suggest that metaboli sm may involve several monooxygenase isoforms. (C) 1995 Academic Press , Inc.