Nitrate reductase complex of Escherichia coli K-12: isolation and characterization of mutants unable to reduce nitrate.

Thirty-eight mutants unable to reduce nitrate were isolated from Escherichia coli and characterized biochemically and genetically. All of the mutants exhibited reduced or insignificant levels of formate dehydrogenase, nitrate reductase, or various combinations of these activities and cytochrome b(1) under conditions which resulted in the production of high levels of these activities by the wild-type parental strains. Most of the mutants reverted readily to wild type, and all mapped within a restricted region on the chromosome linked to the tryptophan genes. It was proposed that nitrate reduction in E. coli was catalyzed exclusively by an organized complex containing formate dehydrogenase, cytochrome b(1), and nitrate reductase.