Net proton transport

S.3.4.2 Phenomenology of Ubiquinol Oxidation to Reduce Cytochrome c with Net Proton Transport... 

FIGURE 10.16 The H+,lO-ATPase of gastric mucosal cells mediates proton transport into the stomach. Potassimn ions are recycled by means of an associated K /Cl cotransport system. The action of these two pnmps results in net transport of and Cl into the stomach. 

The N decay step completes the transport cycle even though the recovery of bacterio-rhodopsin has not yet taken place. Until this point in the photocycle, absorption of a second photon (e.g. by M in the blue-light effect ) defeats the transport process as it recovers bacteriorhodopsin without net proton translocation [137,138]. Absorption of a second photon by N, however, results in completion of the transport cycle and this takes place more rapidly than it does by the thermal route [139]. It appears then that the reactions after N serve simply to recover the chromophore. 

The uncouplers which abolish the coupling of respiratory rate to ATP synthesis act as proton translocators, inducing net proton translocation across the membranes. In this way the proton circuit can be short-circuited , allowing the protons translocated by the generator of to cross back across the membrane without passing through the ATP synthase and producing ATP. The majority of the uncouplers are protonatable, lipophilic compounds with an extensive pi-orbital system which allows the electron of the anionic, de-protonated form to be delocalized [11]. This enhances the permeability of the anionic form in the hydrophobic membrane, and allows the proton translocators to permeate in both their neutral (protonated) and anionic (deprotonated) forms. In this way they can catalyze the net transport of protons... 

Since mitochondrial Ca transport is discussed in depth in Chapter 9, this section will be restrict to a brief summary of the way in which the proton circuit can be diverted into accumulating and regulating the transport of the cation, and how the permeation of weak acids is linked indirectly to net Ca transport. 

The activity of this transporter which catalyzes net movements of adenine nucleotides is mentioned here in connection with the electrogenic adenine nucleotide exchange carrier, although it is likely to be a proton-compensated electroneutral exchanger. No counter ion has been identified, nor have compensating proton movements been reported in conjunction with the net nucleotide transport. Also, no influence of ApH on steady state total nucleotide levels has been reported. 

As the acidic groups need to dissociate for the proton to become mobile, one can expect that the water content of the membrane will also have a strong influence on conductivity. Proton transport occms either via hopping of protons from one water molecule to the next (Grotthus mechanism) or via the net transport of HsO or other aggregates of water and [19]. Evidently, as... 

The reduction of ubiquinone by receipt of two electrons to produce within the lipid bilayer membrane, but yet on the matrix side, would allow the pick up of two protons from the matrix. The process would result from formation of the negatively charged whereby the competition for hydration due to the apolar-polar repulsive free energy of hydration, AGap, would open an aqueous channel to the matrix side of the membrane for entry of two protons, 2H. With the above-preferred location for reaction (8.9b) combined with the just noted location of reaction (8.9c), there would be a net transport of two protons from the matrix side to the cytoplasmic side of the membrane. This would be in keeping with the direction of proton transport for Complexes I, III, and IV. As shown below in Figures 8.8 and 8.9, however, transport could not occur by this... 

When a positive voltage is applied to the anode, H2 is oxidized to protons and electrons H2 2H + 2e . Protons transport through the membrane and combine with electrons to form H2 at the cathode 2H -l- 2e — H2. The net reaction is... 

CGMD simulations have become a viable tool in studying self-organization processes in catalyst layers of PEFCs. Stmctural parameters of interest for such studies involve composition and size distributions of Pt/C agglomerates, pore space morphology, surface wettability, as well as the structure and distribution of ionomer. The latter aspect has important implications for electrochemically active area, proton transport properties, and net electrocatalytic activity of the CL. 

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