Azo- and nitro-reductases of the cestode Moniezia expansa. Substrate specificity, reaction products and the effects of flavins and other compounds.

1. The effects of various inhibitors and activators on the azo- and nitro-reductases of Moniezia expansa have been studied. Both reductions were partially inhibited by FAD, FMN, riboflavin, allopurinol, dicoumarol, 5-nitro-2-furaldehyde, azide and cyanide at 1 mM. Both reactions were stimulated by hypoxanthine. Menadione, nitrofurantoin, SKF 525-A (2-diethylaminoethyl 2,2-diphenylvalerate) and fluoride were without effect. 2. Xanthine- and aldehyde-oxidase activities were not detected in the enzyme preparation. 3. The substrate specificity of the azo- and nitro-reductases were determined. Azobenzene, 4-dimethylamino-azobenzene and 1,2-dimethyl-4-(4-carboxyphenylazo)-5-hydroxybenzene, nitrobenzene, 4-nitrohippuric acid and the isomers of nitrophenol, nitroanisole, nitrobenzoic acid, nitrobenzaldehyde and nitrobenzyl alcohol were reduced. Nitrobenzaldehyde isomers were not reduced to the alcohols and the coumaric acids were not reduced to the phenylpropionic acids. 4. The products of azo- and nitro-reduction were the corresponding amines; hydroxylamino- and hydrazo-compounds were not detected. 5. The pH optima and cofactor requirements were the same for both azo- and nitro-reduction. Neither reaction was inhibited by oxygen.