Potential electrogenic

Although this feature offers the means to eliminate B, if undesirable, by appropriate choice of potential, it also demonstrates possible failure to observe certain products in electrocatalytic studies at conventional electrolytic potentials. For instance, product B is formed in Fig. 34 under slow external transport only at positive reduction potentials electrogeneratively the potential of B appearance shifts to uncoventional, more positive potentials for reductions as the mass transfer coefficient becomes smaller... 

Normally, Na+ reabsorbed via the Na+/K+/2C1 transporter is transported back into the blood by a Na+/K+-ATPase exchange mechanism and by a Na+/Cl cotransporter, the excess Cl returning to the blood via passive diffusion. High intracellular K+ results in its back-diffusion across the luminal membrane, providing a positive potential (electrogenic) that drives reabsorption of both Ca2+ and Mg2+. 

Electrogenic antiport, ADP uptake favored by the membrane potential can also mediate electroneutral exchange of ADPout for... 

The influence of these phenolic acids on electrical potentials may reflect effects on either the diffusion potential or the electrogenic potential of plant root cells. Influence on the electrogenic component could result from inhibition of ATPases which generate the electrogenic component or from reductions in the substrate (ATP) for the ATPases. 

From the point of view of the stoichiometry of the transported ions during active transport, the electroneutral pump, where there is no net charge transfer or change in the membrane potential, must be distinguished from the electrogenic pump connected with charge transfer. 

The difference in the hydrogen ion electrochemical potential, formed in bacteria similarly as in mitochondria, can be used not only for synthesis of ATP but also for the electrogenic (connected with net charge transfer) symport of sugars and amino acids, for the electroneutral symport of some anions and for the sodium ion/hydrogen ion antiport, which, for example, maintains a low Na+ activity in the cells of the bacterium Escherichia coli. 

Figure 2. Sodium and chloride uptake across an idealised freshwater-adapted gill epithelium (chloride cell), which has the typical characteristics of ion-transporting epithelia in eukaryotes. In the example, the abundance of fixed negative charges (muco-proteins) in the unstirred layer may generate a Donnan potential (mucus positive with respect to the water) which is a major part of the net transepithelial potential (serosal positive with respect to water). Mucus also contains carbonic anhydrase (CA) which facilitates dissipation of the [H+] and [HCO(] to CO2, thus maintaining the concentration gradients for these counter ions which partly contribute to Na+ import (secondary transport), whilst the main driving force is derived from the electrogenic sodium pump (see the text for details). Large arrow indicates water flow...

A third, clearer explanation of the electron transfer, proton translocation cycle is given by Saratse. Each ubiquinol (QH2) molecule can donate two electrons. A hrst QH2 electron is transferred along a high-potential chain to the [2Fe-2S] center of the ISP and then to cytochrome Ci. From the cytochrome Cl site, the electron is delivered to the attached, soluble cytochrome c in the intermembrane space. A second QH2 electron is transferred to the Qi site via the cytochrome b hemes, bL and bn. This is an electrogenic step driven by the potential difference between the two b hemes. This step creates part of the proton-motive force. After two QH2 molecules are oxidized at the Qo site, two electrons have been transferred to the Qi site (where one ubiquinone (Qio) can now be reduced, requiring two protons to be translocated from the matrix space). The net effect is a translocation of two protons for each electron transferred to cytochrome c. Each explanation of the cytochrome bci Q cycle has its merits and its proponents. The reader should consult the literature for updates in this ongoing research area. 

Transport by ASBT is electrogenic with a 2 1 ratio of Na rbile acids and membrane potential may regulate transport function. ASBT is essential for the enterohepatic circulation as shown by ASBT gene knockout mice that developed bile-acid malabsorption with no enterohepatic circulation. This is summarised in Figure 2.4. 

Fig. 10. Interaction of the ions with protein-in-the-membrane in the Fq portion of ATP synthase. Black dots are protons the negative charge represents the Asp-61 residue in the c subunit. rp is 120 mV for the electrogenic case or 60 mV for the dynamically electrogenic, overall electroneutral case discussed in the text. In the left most panel, the -rp potential has been created either by the redox enzymes or by organic anions respectively. Following the rightmost arrow, a state is reached (not shown) when the entire potential has been discharged. This potential is re-created, and the cycle repeats...

Electrogenerative synthesis, 1377 Electrogrowth of metals on electrodes, 1293 see also Electrodeposition Electrokinetic potential, 1069... 

Because three Na+ ions move outward for every two K+ ions that move inward, the process is electrogenic—it creates a net separation of charge across the membrane. The result is a transmembrane potential of —50 to —70 mV (inside negative relative to outside), which is characteristic of most animal cells and essential to the conduction of action potentials in neurons. The central role of the Na+K+ ATPase is reflected in the energy invested in this single reaction about 25% of the total energy consumption of a human at rest ... 

Neurons oxidize glucose by glycolysis and the citric acid cycle, and the flow of electrons from these oxidations through the respiratory chain provides almost all the ATP used by these cells. Energy is required to create and maintain an electrical potential across the neuronal plasma membrane. The membrane contains an electrogenic ATP-driven antiporter, the Na+K+ ATPase, which simultaneously pumps 2 K+ ions into and 3 Na+ ions out of the neuron (see Fig. 11-37). The resulting... 

K+-ATPase is the primary source of the membrane potential for most eukaryotic cells and is said to be electrogenic. Because the cell membrane is somewhat permeable to K+, outward diffusion of K+ through the "leaky" membrane along its concentration gradient helps to maintain the membrane potential as does inward leakage of CP. At the same time, Na+ diffuses inward, aided by the membrane potential. Even though the permeability of Na+ is low, a steady state is reached at which the rate of passive inward diffusion of cations just balances the membrane potential set up by the active transport. 

Electrode potentials 300 - 302 measurement of 302 observed 301 standard, table 300 Electrogenic 423... 

Differentiate between electrogenic and neutral transport systems in mitochondria. How is electrogenic transport influenced by the membrane potential ... 

For each ATP that it splits, the Na+-K+ pump moves three Na+ ions out of the cell and brings in two K+ ions. This means that the pump is intrinsically electrogenic It creates an electric potential gradient across the membrane... 

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