Mitchell s chemiosmotic theory

Mitchell s chemiosmotic theory postulates that the energy from oxidation of components in the respiratory chain is coupled to the translocation of hydrogen ions (protons, H+) from the inside to the outside of the inner mitochondrial membrane. The electrochemical potential difference resulting from the asymmetric dis-... 

Mitchell s chemiosmotic theory [68-70] is generally accepted (see reviews in Refs. 5,37 and 71), though a large number of important details are still undefined, including the mechanism of action of the ATP synthase itself, and the ratio of ATP formed to electron transported. 

Proton motive ATP synthesis in FqF, liposomes (Fig. 5.1, Table 5.4) and AjEtH -driven translocation through Fg [6] strongly supported Mitchell s chemiosmotic theory described in the previous series of Comprehensive Biochemistry [108]. The molecular mechanism of function of FgF, was not predicted by this theory, but it has been elucidated by new methods. For example, the presence of X-P was demonstrated in... 

In this chapter, we will describe the composition of the phosphorylating enzyme of chloroplasts as determined by SDS-gel electrophoresis and its structure as revealed by electron microscopy. These studies led to a preliminary model for the chloroplast ATP synthase. The remainder of the chapter will be devoted to two main topics (photo)phosphorylation powered by proton translocation as described by Mitchell s chemiosmotic theory V and recent investigations of the structure and function of the phos-phorylating enzyme in relation to Paul Boyer s binding-change mechanism and a model involving... 

According to Mitchell s chemiosmotic theory, photophosphorylation is driven by energy derived from electron transfer coupled to proton translocation. The results of postillumination discussed in the previous section further supports the notion that a proton gradient is the driving force for phosphorylation. It is therefore possible in principle that a similar proton gradient produced by artificial means might also be able to drive phosphorylation in a chloroplast membrane, entirely in the dark, i. e., without the aid of photo-induced electron transport. Such a scheme was indeed realized by the so-called acid-bath ATP-forma-tion demonstrated by Jagendorf and Uribe " in 1966. 

Figure 18-13 Principal features of Mitchell s chemiosmotic theory of oxidative phosphorylation.

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-... 

According to Mitchell s chemiosmotic theory [52,53] active transport, oxidative phosphorylation and ATP synthesis are driven by a protonmotive force which is made up of two components an electrical potential gradient and a pH gradient across the cell membrane. Agents which conduct ions across the membrane destroy the pH gradient and thereby reduce the protonmotive force. It is possible to measure the pH gradient and to monitor its attenuation by... 

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