ИСТИНА

Escherichia coli is known to couple aerobic respiratory catabolism to ATP synthesis by virtue of the three primary proton-motive force (pmf) generators: NADH dehydrogenase I (NDH-I), cytochrome bo3, and cytochrome bd-I. The non-pumping, copper-lacking three-heme bd-type oxidase couples oxidation of quinol to reduction of O2 to H2O. Nevertheless, E. coli mutant strains deficient in NDH-I, bo3, and bd-I can grow under aerobic and glucose-limited conditions, although its sole terminal oxidase cytochrome bd-II was proposed to be nonelectrogenic. In the present work, the ability of cytochrome bd-II to generate pmf is reexamined. Absorption and fluorescence spectroscopy and oxygen pulse methods all show that in the steady-state, cytochrome bd-II is capable of producing both electrical and chemical components of pmf yielding H+/e− ratio of 0.94±0.18; this is sufficient to drive ATP synthesis and transport of nutrients. Microsecond time-resolved, single-turnover electrometry provides evidence for a molecular mechanism of the proton motive force production. The ability to induce cytochrome bd-II biosynthesis allows E. coli to remain energetically competent under a variety of environmental conditions, particularly at the extremely low oxygen pressure and carbon and phosphate starvation.