Summary: Mutants of K12 have been isolated which reduce nitrite 3 to 30% as rapidly as the wild-type. Activities of reduced nicotinamide adenine dinucleotide (NADH)-nitrite oxidoreductase were lower in cell-free extracts of these mutants than in the wild-type. The mutants grew on minimal agar, and their sulphite reductase activity was the same as in the wild-type.

Double mutants deficient in both nitrite and sulphite reductases were constructed, as well as recombinants which had regained one or both activities following recombination with Hfr Hayes. The inability to reduce sulphite was due to an altered † gene. Suspensions of and bacteria reduced nitrite at similar rates, showing that sulphite reductase (which is a gratuitous nitrite reductase) contributes little to the rate of nitrite reduction Cytochome was synthesized by double recombinants but not by or bacteria. This data suggests that cytochrome is involved in nitrite reduction in either as a component of NADH-NO oxidoreductase, or as an electron carrier whose synthesis is affected by the gene.


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