4-Nitrobenzoic acid reductase of the nematode Ascaris lumbricoides var suum. Localization of the enzyme and optimum assay conditions.

1. Reduction of 4-nitrobenzoic acid by the nematode Ascaris lumbricoides var suum occurred in the intestinal brush border cells. Cuticle, mesenchyme fluid and reproductive tissue showed no activity. 2. 4-Nitrobenzoic acid reductase was in the supernatant fraction after centrifugation of intestinal homogenates at 75 000 g for 2 h. 3. The enzyme required as cofactors NADH2, a low molecular weight thiol such as glutathione or cysteine and a divalent metal ion such as Mn++ or Cu++. The reduction was not catalysed by NADPH2. 4. Reduction was not inhibited by O2 or CO. Optimum pH of the reaction was about 6.5.