A terminal oxidase that produces a proton motive force by the vectorial transfer of protons across the inner membrane. It is the component of the aerobic respiratory chain of E.coli that predominates when cells are grown at low aeration. Generates a proton motive force using protons and electrons from opposite sides of the membrane to generate H(2)O, transferring 1 proton/electron. 2 a ubiquinol + 4 H(+)(in) + O2(in) = 2 a ubiquinone + 4 H(+)(out) + 2 H2O(in) Binds 1 protoheme IX center (heme b558). Binds 1 protoheme IX center (heme b595) per heterodimer, in conjunction with CydB. Binds 1 iron-chlorin (heme d or cytochrome d) per heterodimer, in conjunction with CydB. Energy metabolism; oxidative phosphorylation. Heterodimer of subunits I and II. Belongs to the cytochrome ubiquinol oxidase subunit 1 family. Extended N-terminus. Extended N-terminus.