Proton, energies gradient

Fig. 6.9 The catalysts for denitrification. Nitrate is reduced by a molybdenum enzyme while nitrite and oxides of nitrogen are reduced today mainly by copper enzymes. However, there are alternatives, probably earlier iron enzymes. The electron transfer bct complex is common to that in oxidative phosphorylation and similar to the bf complex of photosynthesis, while cytochrome c2 is to be compared with cytochrome c of oxidative phosphorylation. These four processes are linked in energy capture via proton (H+) gradients see Figure 6.8(a) and (b) and the lower parts of Fig. 6.9 which show separately the active site of the all iron NO-reductase, and the active site of cytochrome oxidase (02 reductase).

F-ATPases (including the H+- or Na+-translocating subfamilies F-type, V-type and A-type ATPase) are found in eukaryotic mitochondria and chloroplasts, in bacteria and in Archaea. As multi-subunit complexes with three to 13 dissimilar subunits, they are embedded in the membrane and involved in primary energy conversion. Although extensively studied at the molecular level, the F-ATPases will not be discussed here in detail, since their main function is not the uptake of nutrients but the synthesis of ATP ( ATP synthase ) [127-130]. For example, synthesis of ATP is mediated by bacterial F-type ATPases when protons flow through the complex down the proton electrochemical gradient. Operating in the opposite direction, the ATPases pump 3 4 H+ and/or 3Na+ out of the cell per ATP hydrolysed. 

What do I mean by a proton concentration gradient Simply, there is a higher concentration of protons in the space between the inner and outer membranes of the mitochondrion than in the mitochondrial interior. The gradient is formed from the energy released in the transfer of electrons down the electron transport chain. Put another way, the released energy is employed to pump protons across the inner mitochondrial membrane into the intermembrane space. 

Oxidative phosphorylation is ATP synthesis linked to the oxidation of NADH and FADH2 by electron transport through the respiratory chain. This occurs via a mechanism originally proposed as the chemiosmotic hypothesis. Energy liberated by electron transport is used to pump H+ ions out of the mitochondrion to create an electrochemical proton (H+) gradient. The protons flow back into the mitochondrion through the ATP synthase located in the inner mitochondrial membrane, and this drives ATP synthesis. Approximately three ATP molecules are synthesized per NADH oxidized and approximately two ATPs are synthesized per FADH2 oxidized. 

Cytochrome oxidases. Mitochondrial cytochrome c oxidase uses the energy involved in the oxidation of cytochrome c and reduction of water to generate a proton electrochemical gradient across the inner mitochondrial membrane [57], As stated above, a ferryl state is an essential intermediate in this process. Similar intermediates are to be expected in all similar proton-translocating cytochrome oxidases that contain a binuclear haem-copper centre,... 

Energy is provided, for example, by ATP for pumping sodium ions out of and potassium ions into the cell. Another important example of primary active transport is the proton concentration gradient driven ATP synthesis (Mitchell-hypothesis). 

Electrogenic, involving an exchange between anions of different charges (which requires energy as membrane potential or proton electrochemical gradient)... 

Complex 1, which transfers electrons from the matrix NAD /NADH pool to the membrane-bound pool of ubiquinone/ubiquinol operates close to equilibrium such that the energy lost by the electrons (some 300 meV) is conserved in the proton electrochemical gradient. As a result, three protons can be extruded by this complex for the passage of two electrons [23]. 

Proton-transfer reactions of iV-tetrachlorosalicylideneaniline (140) and N-tetrachlorosalicylideneaniline-l-pyrenylamine (171) have been investigated by using a semiempirical self-consistent field molecular orbital (SCF MO) method with an energy gradient technique.94 From the calculated potential barriers (81.27 and 87.30kJmol-1) for 140 and 171, respectively, it can be seen that the... 

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