7.1.1.7 cytoplasm the cytochrome bd-I complexis concentrated in mobile patches in the plasma membrane 5737 725995 7.1.1.7 membrane - 16020 743604, 752197 7.1.1.7 membrane subnit cydA has nine transmembrane helices with the O2 reactive site near the periplasmic surface. Residue His19, the ligand to the high spin heme b595 component of the oxidase, is located near the periplasmic surface of the protein 16020 727505