Artificial proton pump

ARTIFICIAL PHYTANYL-CHAINED GLYCOLIPID VESICLE MEMBRANES WITH LOW PROTON PERMEABILITY ARE SUITABLE FOR PROTON PUMP RECONSTITUTION MATRICES... 

In this paper, we will describe one of examples, where artificial archaeal glycolipids are applied to the construction of nano-devices containing energy-conversion membrane proteins, by employing the phytanyl-chained glycolipid we have recently developed, i.e., l,3-di-o-phytanyl-2-o- ((3-D-maltotriosyl) glycerol (Mab (Phyt)2, Fig. 1) [16,17] and natural proton pump, bacteriorhodopsin (BR) derived from purple membranes of the extremely halophilic archaeon Halobacterium salinarium S9 [18],... 

These significant findings form the basis of a set of design principles for the construction of molecular photovoltaic cells and other nanoscale electronic devices in which the control of both the rate and directionality of ET processes is an essential requirement. The successful construction of an artificial light-driven proton pump, based on principles of long-range ET processes illustrates the promise of this approach.1501... 

A crucially important finding is that submitochon-drial particles or vesicles from broken chloroplasts will synthesize ATP from ADP and P , when an artificial pH gradient is imposed.172186 Isolated purified FjF0 ATPase from a thermophilic Bacillus has been coreconstituted into liposomes with the light-driven proton pump bacteiiorhodopsin (Chapter 23). Illumination induced ATP synthesis.187 These observations support Mitchell s proposal that the ATP synthase is both spatially separate from the electron carriers in the membrane and utilizes the protonmotive force to make ATP. Thus, the passage of protons from the outside of the mitochondria back in through the ATP synthase induces the formation of ATP. What is the stoichiometry of this process ... 

The ATP synthase is a reversible proton-translocating ATP ase The initial experiments which were important for the verification of the chemiosmotic hypothesis were those which showed that the complex was an autonomous proton pump when hydrolyzing ATP, and which showed that an artificial A/a could cause the ATP synthase to generate ATP. Thus, if a limiting amount of ATP is injected into an anaerobic mitochondrial incubation a net expulsion of protons is observed, followed by a decay which is accelerated by proton translocators [15]. Less complications arise if the experiment is repeated with inverted sub-mitochondrial... 

As in the case of the ATP synthase, the most convincing evidence for the function of the respiratory chain as an autonomous proton pump comes from the ability to purify energy-conserving segments of the chain and reconstitute them into artificial bilayers with the recovery of their proton translocating capacity [21,22]. 

Complex IV - Complex IV is also known as cytochrome oxidase, because it takes electrons from cytochrome c. Complex IV contains cytochromes a and a3. Cytochromes a and a3 evidently represent two identical heme A moieties, attached to the same polypeptide chain. They are within different environments in the inner membrane, however, so they have different reduction potentials. Each of the hemes is associated with a copper ion, located close to the heme iron. Electrons that pass through complex IV can be blocked by cyanide, azide, and carbon monoxide and the artificial electron carrier, ferricyanide, can accept electrons from cytochrome a in the complex (Figure 15.9). A model for the final stages in proton pumping by cytochrome oxidase is shown in Figure... 

Figure C3.2.17. Diagram of a liposome-based artificial photosynthetic membrane showing the photocycle that pumps protons into the interior of the liposome and the CFqF j-ATP synthase enzyme. From [55],...

A prediction of the chemiosmotic theory is that, because the role of electron transfer in mitochondrial ATP synthesis is simply to pump protons to create the electrochemical potential of the proton-motive force, an artificially created proton gradient should be able to replace electron transfer in driving ATP synthesis. This has been experimentally confirmed (Fig. 19-20). Mitochondria manipulated so as to impose a difference of proton concentration and a separation of charge across the inner membrane synthesize ATP in the absence of an oxidizable substrate the proton-motive force alone suffices to drive ATP synthesis. 

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