KEMP, JOHN D. (University of California, Los Angeles), AND DANIEL E. ATKIN-SON. Nitrite reductase of Escherichia coli specific for reduced nicotinamide adenine dinucleotide. J. Bacteriol. 92:628-634. 1966.-A nitrite reductase specific for reduced nicotinamide adenine dinucleotide (NADH2) appears to be responsible for in vivo nitrite reduction by Escherichia coli strain Bn. In extracts, the reduction product is ammonium, and the ratio of NADH2 oxidized to nitrite reduced or to ammonium produced

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... s 3. The Michaelis constant for nitrite is 10 ,uM. The enzyme is induced by nitrite, and the ability of intact cells to reduce nitrite parallels the level of NADH2-specific nitrite reductase activity demonstrable in cell-free preparations. Crude extracts of strain Bn will also reduce hydroxylamine, but not nitrate or sulfite, at the expense of NADH2. Kinetic observations indicate that hydroxylamine and nitrite may both be reduced at the same active site. The high apparent Michaelis constant for hydroxylamine (1.5 mM), however, seems to exclude hydroxylamine as an intermediate in nitrite reduction. In vitro activity is enhanced by preincubation with nitrite, and decreased by preincubation with NADH2. ,umole; KNO2, 2.0 umoles; and enzyme preparation containing 0.5 to 1.0 mg of soluble protein. All results reported were obtained under conditions in which rate 628 Vol. 92, No. 3