The aerobic respiratory chain of Escherichia coli

The aerobic respiratory chain of Escherichia coli couples the oxidation of organic substrates, such as succinate, to the generation of a proton motive force across the cytoplasmic membrane. The mechanism by which this is accomplished is quite different than found in the mitochondrial respiratory system, as predicted by D. Keilin¹ nearly 50 years ago. Aerobically grown E. coli has no cytochrome c, and no equivalent to the mitochondrial Complex III (bc₁ complex) or Complex IV (cytochrome c oxidase). Instead, two enzymes in the E. coli cytoplasmic membrane, the cytochrome o and cytochrome d complexes, oxidize ubiquinol and directly reduce molecular oxygen to water, concomitantly generating an electrochemical proton gradient across the membrane.