Hydroxylamine oxidoreductase of Nitrosomonas. Oxidation of diethyldithiocarbamate concomitant with stimulation of nitrite synthesis

Although nitrate was not produced in the oxidation of ammonia or hydroxylamine as catalyzed by intact cells, hydroxylamine oxidoreductase from Nitrosomonas europaea catalyzed the aerobic oxidation of hydroxylamine to nitrite and nitrate. The reaction was most rapid in the presence of added electron acceptor. Nitrate was not produced from nitrite. The precursor of nitrate was an N-oxide of oxidation state between hydroxylamine and nitrite. In the presence of diethyldithiocarbamate, hydroxylamine was oxidized to nitrite but nitrate was not produced. For each mol of nitrite produced, approximately 1 mol of diethyldithiocarbamate was oxidized to bis(diethyldithiocarbamoyl)disulfide (Disulfiram). Oxidation of diethyldithiocarbamate required the concomitant oxidation of hydroxylamine. The enzyme did not catalyze the direct oxidation of diethyldithiocarbamate utilizing oxygen, H2O2, nitrite, nitrate or PMS as electron acceptor. The effect of structural analogs of diethyldithiocarbamate suggested that diethyldithiocarbamate was effective because it bound to a metal ion and had an oxidizable SH group. Diethyldithiocarbamate may act by either (a) reducing a reactive form of oxygen generated during the oxidation of hydroxylamine thus preventing the oxidation of an N-compound to nitrate, or (b) reducing an N-containing precursor of nitrate to an N-compound which was subsequently oxidized to nitrite. Methods for the assay of diethyldithiocarbamate are described.