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 endogenous substrates (cinnamic acid and lauric acid), three organophosphate insecticides (diazinon, isazofos, and methidathion), three acetamide herbicides (metolachlor, CGA-24704, and alachlor), and bentazon. Cinnamic acid was aryl hydroxylated forming p-coumaric acid. Lauric acid was pamarily hydroxylated at the terminal carbon (omega hydroxylation). The three alpha-chloroacetamides were O-demethylated. With all three organophosphate insecticides. the phosphorothionate sulfur was oxidized to the corresponding oxon and the phosphoroester oxygen was cleaved in both diazinon and isazofos. Bentazon was aryl hydroxylated forming the 6-hydroxy derivative. The concentration of cytochrome P450 in the 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 increased with the combination of NA, clofibrate, and ethanol. The extent of metabolism of only lauric acid paralleled the increases in cytochrome P450 content. The various seed/seedling treatments, however, did approximately double the rate of metabolism of the three organophosphates, the three chloroacetamides, and bentazon. Metabolism required a reduced pyridine nucleotide and was affected by several cytochrome P450 monooxygenase inhibitors (carbon monoxide, tetcyclacis, piperonyl butoxide, 1-aminobenzotnazole, and SKF-525A). The inhibitors differentially affected metabolism of the substrates. Microsomal oxidations from both untreated and inducer-treated tissue responded similarly to the inhibitors. The differential inhibitory responses suggest that metabolism may involve several monooxygenase isoforms.