Movement of protons

Chow, W.S., Thome, S.W., Boardman, N.K. The movement of protons during energy transduction in the chloropiast thylakoid membrane. In Light Transducing Membranes (Deamer, D.W., ed.). New York, San Francisco, London Academic Press 1978, pp. 253-268... 

Changes in pH are propagated by the movement of protons. Bnt because free protons do not exist they must move by transfer between proton donors and acceptors, i.e. Bronsted acids and bases ... 

The first model to describe the membrane in the above fashion was that of Bernardi and Verbrugge, "° which was based on earlier work by Verbrugge and Hill. " 214 model utilized a dilute solution approach that used the Nernst— Planck equation (eq 29) to describe the movement of protons, except that now v is not equal to zero. The reason is that, because there are two phases, the protons are in the water and the velocity of the water is give by Schlogl s equation ... 

B. The pH gradient is used to drive ATP synthesis by the movement of protons back to the matrix through a transmembrane protein complex, or ATP synthase. 

The picture begins to come somewhat into focus. Starting off with some basic mechanics of electrons, one was able to define the quantum mechanical condition for the tunneling of electrons from a metallic donor to electron acceptors through an electron-energy barrier. The tunneling condition could be expressed in terms of an energy barrier for ion movement, e.g., the movement of protons toward the metal in the reaction ... 

Electron-transferring molecules in the chain of carriers connecting PSII and PSI are oriented asymmetrically in the thylakoid membrane, so photoinduced electron flow results in the net movement of protons across the membrane, from the stromal side to the thylakoid lumen (Fig. 19-57). In 1966 Andre Jagendorf showed that a pH gradient across the thylakoid membrane (alkaline outside) could furnish the driving force to generate ATP. 

FIGURE 20-17 Source of ATP and NADPH. ATP and NADPH produced by the light reactions are essential substrates for the reduction of C02. The photosynthetic reactions that produce ATP and NADPH are accompanied by movement of protons (red) from the stroma into the thylakoid, creating alkaline conditions in the stroma. Magnesium ions pass from the thylakoid into the stroma, increasing the stromal [Mg2+],... 

What are the chemical structures of the intermediates in Eq. 23-37, and why are there so many of them The answer to the last question is that the initial photochemical process is very fast. Subsequent conformational rearrangments and movement of protons are slower, occur in distinct steps, and give rise to the observed series of intermediates. To shed light on these processes many experiments have been done with analogs of retinal,502,505 508 often using very rapid spectroscopic techniques.37,508 These studies have shown that the isomerization of the Schiff base from... 

How the movement of protons through F0 drives the formation of ATP in F, is not known. However, studies by Paul Boyer, Harvey Penefsky, and others have shown that the enzyme binds ADP and ATP very tightly. The reaction... 

The combined effect of exchanging extramitochon-drial ADP-3 and H2P04 for mitochondrial ATP-4 and OH is to move one proton into the mitochondrial matrix for every molecule of ATP that the mitochondrion releases into the cytosol. This proton translocation must be considered, along with the movement of protons through the ATP synthase, to account for the P-to-O ratio of oxidative phosphorylation. If three protons pass through the ATP synthase, and the adenine nucleotide and Pj transport systems move one additional proton, then four protons in total move into the matrix for each ATP molecule provided to the cytosol. 

Flow of protons back into the bacterial cell, down the electrochemical potential gradient, is mediated by an ATP-synthase resembling the ATP-synthase of the mitochondrial inner membrane (see chapter 14). As in mitochondria, the movement of protons through the F0 base-piece of the enzyme drives the formation of ATP (see fig. 15.13). 

The structure of aqueous solutions depends on the following parameters 1. content of H-bonds of water molecules, 2. interactions water-solute, 3. orientations of H-bonds, 4. H-bond distances, 5. life-time of H-bonds, 6. movement of protons in acids or defect-protons in bases. There are some computer experiments with water and a model of ions78. They show a separation of the ions in 1 psec but that the distance of ions remains about 5 A78. This gives a simple interpretation of the optical constancy of absorbing ions independantly from the concentration79. ... 

In mitochondria there are two types of mechanisms for coupling the electron transport to the movement of protons across the membrane. The first is based on anisotropic reduction and oxidation of a lipid-soluble quinone inside the membrane. The quinone, coenzyme Q, becomes protonated upon reduction and diffuses to an oxidation site on the other side of the membrane where removal of electrons leads to proton release. This is essentially a proton carrier system with the hydroquinone acting as the proton carrier in the lipid phase of the membrane. A further refinement of this system in mitochondria provides for a coenzyme Q redox cycle where the movement of one electron through the chain allows for two protons to cross the... 

Figure 17.2 The chemiosmotic hypothesis. Electrons from NADH and/or FADH2 are passed to Oz via the electron transport chain. In the process, protons are extruded into the mitochondrial intermembrane space. The proton gradient thus created causes the movement of protons back into mitochondria through a channel in the F ATPase. In the process, one molecule of ATP is formed frm ADP and phosphate for every two to three protons channeled back into the mitochondria. ATP moves into the intermembrane space and cytosol in exchange for ADP moving in the opposite direction. Phosphate is taken up in exchange for OH".

Finish Partially Solved Problem 6-1 by showing how the rearranged carbocations give the four products shown in the problem. Be careful when using curved arrows to show deprotonation and/or nucleophilic attack by the solvent. The curved arrows always show movement of electrons, not movement of protons or other species. 

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