Biochemical studies on the catalysis of nitrosation by bacteria

Abstract

Biochemical and microbiological studies were conducted to characterize the mechanism of bacterial formation of N-nitrosomorpholine from morpholine and nitrite at neutral pH. Nitrosating activity was markedly induced when bacteria were cultured anaerobically in minimal culture medium containing nitrate, while the presence of cysteine or tungsten in the medium inhibited induction. Of various metals, coenzymes and inhibitors tested for their effects on in vitro nitrosation of morpholine, potassium cyanide, sodium azide, NAD(P)H and nitrate strongly inhibited nitrosation. Several mutants of Escherichia coli A10 strain were prepared in order to examine whether nitrosation activity is linked to specific loci. Niridazole-resistant mutants, which lack nitroreductase, had as much nitrosating activity as the original E. coli A10, but chlorate-resistant mutants had completely lost this activity. A good correlation was observed between nitrate reductase activity and nitrosating activity in these mutants. These results indicate that bacterial nitrosation is an enzyme-mediated reaction closely associated with molybdenoenzymes such as the nitrate reductase/formate hydrogenlyase system.