Mitchell’s theory

A competing model called the chemiosmotic model was suggested by Mitchell in 1961 and won a Nobel prize. The physical events that which Mitchell s theory implies are less consistent with modem concepts of interfacial charge transfer than those of Williams, which do indicate interfacial charge transfer. 

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. 

The experimental use of artificial electron acceptors and donors has demonstrated, in agreement with Mitchell s theory, that electron transport can be coupled to ATP synthesis only when the chemical structure and the lipophilicity of the electron carriers added is such as to allow vectorial proton transport across the membrane [72]. 

Since both terms on the right-hand side are vectors, A/IH+ too is a vector motive force. In Mitchell s theory it is the membrane which is the essential condition for the vector nature of the flow. ApH refers to the bulk of the aqueous phases in contact with the membrane. 

The next important postulate of Mitchell s theory concerns the consumers of the energy produced by primary pumps and presupposes the presence in the organella membranes of secondary proton pumps which use the transmembrane proton flow for ATP synthesis and a number of other processes. Essential to this theory is the... 

Mitchell s theory was always a phenomenological theory. He himself tried to outline some of the basic features of the mechanism,168 but his attempt could hardly be described as successful. 

Yet in the very same year that Mitchell s theory appeared, Williams formulated the concept of a localized proton processing with the main emphasis on local interactions.138... 

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