Abstract
Flavin-containing monooxygenase (FMO) is an important microsomal enzyme which may affect the toxicity of nitrogen and sulfur-containing chemicals such as organophosphate and carbamate pestcides encountered by aquatic organisms. FMO activity as determined via N,N-dimethylaniline (DMA) N-oxide formation was observed and characterized in liver microsomes from rainbow trout ( Oncorhynchus mykiss) Microsomal DMA N-oxidase activity was optimal at pH 8.4–9.2, 20°C and required NADPH. Addition of the cytochrome P-450 inhibitor, N-benzylimidazole failed to alter DMA N-oxidase activity but coincubation with methimazole, trimethylamine (TMA) or aldicarb significantly inhibited DMA oxidase. DMA oxidase demonstrated Michaelis-Menten kinetics and was competitively inhibited by TMA and aldiearb. These data suggest that aldicarb and TMA are substrates for FMO and that cytochronie P-450 plays no role in the N-oxidation of DMA in this organism.
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