Mitchell electrochemical gradients

Peter Mitchell s chemiosmotic hypothesis revolutionized our thinking about the energy coupling that drives ATP synthesis by means of an electrochemical gradient. How much energy is stored in this electrochemical gradient For the transmembrane flow of protons across the inner membrane (from inside [matrix] to outside), we could write... 

Peter Mitchell (Nobel Prize, 1978) of Great Britain was the first to realize, and to propose in his chemi-osmotic theory, that the energy required for die ADP-ATP reaction could be derived by an accretion of protons in the thylakoid sac to the point at which the electrochemical gradient across the membrane could effect the proton transport required as die driving force for this reaction. See also Phosphorylation (Photosynthetic). 

The idea that oxidative phosphorylation and photophosphorylation systems are coupled with the transfer of a proton through the membrane was introduced by Mitchell (1966) and is now widely accepted. H+-ATPase (ATP synthase, F,Fo-ATPase) catalyzes ATP synthesis coupled to an electrochemical gradient and ATP hydrolysis driven by proton translocation in mitochondrial or bacterial membranes. (Boyer, 2001 Babcock and Wikstroem, 1992 Abraham et al., 1994 Allison, 1998 Ogilvie et al. 1997 Musser and Theg, 2000 Backgren et al., 2000 Arechada and Jones, 2001 Gibbsons et. al., 2000 and references therein). The enzyme from Escherichia coli consists of two parts, a water-... 

Active transport processes in cellular membranes are well understood in terms of Mitchell s chemiosmotic theory. The idea that, directly or indirectly, active transport is energized by the electrochemical gradient of protons which is generated by H -ATPase, and that the solute molecules are taken up by symport and antiport processes with as the working ion, has been fully confirmed in the case of plant cells as well. The electrochemical gradient of which, divided by the Faraday con-... 

Peter Mitchell His chemiosmotic hypothesis, wherein ATP was synthesized by an electrochemical gradient of hydrogen ions across bacterial, mitochondrial, and chloroplast membranes, revolutionized bioenergetics. 

Mitchell s theory holds that an electrochemical proton gradient across the membrane (which is only slightly permeable to many ionized species and particularly to H ") is formed by the vectorial transport of into the thylakoid lumen coupled to electron transport, as a consequence of the alternate disposition across the membrane of electron carriers which can bind protons and others which cannot be protonated. 

Two major ATP synthesizing reactions in living organisms are oxidative phosphorylation and photophosphorylation. Both reactions take place in H -ATPase (FqF,), which is driven by an electrochemical potential difference of protons across the biomembrane, as predicted by Mitchell [1]. In Racket s laboratory, ATPases related to oxidative phosphorylation were prepared, but their relationship to Mitchell s chemiosmotic hypothesis [1] was not described [2], Later, an insoluble ATPase (H -ATPase) was shown to translocate protons across the membrane when it was reconstituted into liposomes [3], H -ATPase was shown to be composed of a catalytic moiety called F, (coupling factor 1) [4], and a membrane moiety called Fq [5], which confers inhibitor sensitivity to F,. F was shown to be a proton channel, which translocates down an electrochemical potential gradient across the membrane when Fg is reconstituted into liposomes (Fig. 5.1) [6]. Thus, -ATPase was called FqFj or ATP synthetase. 

In his chemiosmotic theory [52,53] Mitchell proposes that energy derived from respiratory activity, or from substrate level oxidation ( anaerobic metabolism) produces an electrochemical potential ( protonmotive force ) across the cell membrane of bacteria, mitochondria, and chloroplasts. The total protonmotive force is made up from two components an electrical potential gradient and a chemical gradient of protons (i.e. a pH gradient) across the membrane. The protonmotive force provides the energy for the active transport of sugars and amino... 

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