Energy-transducing complexes in bacterial respiratory chains.

Abstract

Oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts are highly organized systems that yield living energy for eukaryotes. By introducing the concept of an electrochemical H+ gradient across the membrane (\(\Delta \tilde \mu \rm H^ + \))—that is, a proton motive force (pmf) composed of ΔΨ and ΔpH as \(\Delta \tilde \mu \rm H^ + _{(mV)} = \Delta \psi - Z\Delta pH\,(Z \simeq 60\,mV)\)—the chemiosmotic hypothesis (Mitchell, 1966) has played a central role in solving the problem of how organelles synthesize ATP using oxidative or photo energy. According to this hypothesis, the components of the electron transfer chain translocate protons across the membrane unidirectionally. The pmf thus established drives protons through an anisotropic reversible proton-translocating ATPase (ATP synthase) to synthesize ATP from ADP and Pi. There are other translocators (H+ symporters such as Pi carrier and electrogenic translocators such as ATP/ADP translocator) in energy-transducing biomembranes that transport substrates using a pmf. These energy-transducing membranes include the cytoplasmic membranes of bacteria. Eubacteria at least (Archaebacteria may have a slightly different ATP synthase) contain the anisotropic F0·F1 type H+-translocating ATPase (ATP synthase) that has very similar molecular architecture and characteristics to those of the ATP synthases of mitochondria and chloroplasts (Amzel and Pedersen, 1983), as well as having several translocators that utilize pmf. In contrast, the bacterial electron transfer chains that produce a pmf show great variety, even if among those in aerobic respiratory systems (Jones, 1977).KeywordsCytochrome OxidaseNADH DehydrogenaseElectron Transfer ChainQuinone OxidoreductaseTerminal OxidaseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.