Identification of subunit I as the cytochrome b₅₅₈ component of the cytochrome d terminal oxidase complex of Escherichia coli

The cytochrome d terminal oxidase complex was recently purified from Escherichia coli membranes (Miller, M.J., and Gennis, R.B. (1983) J. Biol. Chem. 258, 9159-9165). The complex contains two polypeptides, subunits I and II, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and three spectroscopically defined cytochromes, B₅₅₈, a₁, and d. A mutant that failed to oxidize N,N,N',N'-tetramethyl-p-phenylenediamine was obtained which was lacking this terminal oxidase complex and was shown to map at a locus called cyd on the E. coli genome. In this paper, localized mutagenesis was used to generate a series of mutants in the cytochrome d terminal oxidase. These mutants were isolated by a newly developed selection procedure based on their sensitivity to azide. Two classes of mutants which map to the cyd locus were obtained, cydA and cydB. The cydA phenotype included the lack of all three spectroscopically detectable cytochromes as well as the absence of both polypeptides, determined by immunological criteria. Strains manifesting the cydB phenotype lacked cytochromes a₁ and d, but had a normal amount of cytochrome b₅₅₈. Immunological analysis showed that subunit I (57,000 daltons) was present in the membranes, but that subunit II (43,000 daltons) was missing. These data justify the conclusion that subunit I of this two-subunit complex can be identified as the cytochrome b₅₅₈ component of the cytochrome d terminal oxidase complex.