Cell Membranes: Intracellular pH and Electrochemical Potential


Cell metabolism requires transmembrane proton and electrochemical gradients to synthesize adenosine 5′‐triphosphate (ATP), translocate ions, proteins and metabolites and regulate other vital activities.

Keywords: adenosine‐5′‐triphosphate; chemiosmosis; photophosphorylation; oxidative phosphorylation; proton electrochemical potential gradient

Figure 1.

Principles of the chemiosmotic hypothesis. (a) The electron and proton carriers are shown arranged vectorially across the energy‐transducing membrane. (b) Coupled vectorial electron transport and/or ATP hydrolysis by the F‐ATPase deposit protons on the p‐side of the vesicle to increase the pmf. ATP synthesis is driven forward when protons are conducted through the F0 from the p‐side to F1 on the n‐side. Uncouplers equilibrate protons and/or hydroxyl ions across the membrane and dissipate the pmf.

Figure 2.

Typical eukaryotic mitochondrion and chloroplast. The mitochondrion (a) is shown with an enlarged view of the inner membrane and associated respiratory energy‐transducing components. The chloroplast (b) is shown with enlarged view of thylakoid membrane and associated photosynthetic energy‐transducing components. FSP, Rieske iron–sulfur protein; PSI, photosystem I; OEC, oxygen‐evolving complex PC, plastocyanin; FNR, ferredoxin:NADP reductase; PQ, plastoquinone.

Figure 3.

The proton motive Q‐cycle. Grey arrows represent transmembrane movement of ubiquinone (UQ) or UQH2. Dashed and solid arrows trace single or repeated steps, respectively. The symbols n and p represent the negative and positive sides of the inner membrane, respectively. Adapted from Trumpower and Gennis . FSP, Rieske iron–sulfur protein.

Figure 4.

Energetics of eukaryotic respiration (a) and photophosphorylation (b). Boxes represent metalloprotein complexes. The symbols bp and bn represent the respective b‐cytochromes on the n‐ and p‐sides of complex III and b6f. The small arrows trace electron flow within and among complexes and carriers. The large grey arrows in (b) represent the reaction centre electrons following photon absorption. The top horizontal bars of (a) and (b) show for each connected H+ translocating complex (large red arrows) and the integrated (top right). PSI, photosystem I; FNR, ferredoxin:NADP reductase; FSP, Rieske iron–sulfur protein.



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Further Reading

Cramer WA and Knaff DB (1990) Energy Transduction in Biological Membranes. New York: Springer‐Verlag.

Mitchell P (1974) A chemiosmotic molecular mechanism for proton‐translocating adenosine triphosphatases. FEBS Letters 43: 189–194.

Noji H, Yasuda R, Yoshida M and Kinoshita K Jr (1997) Direct observation of the rotation of the F1‐ATPase. [http://www.res.titech.ac.jp/seibutu/nature/f1rotate.html] [http://www.res.titech.ac.jp/seibutu/nature/f1rotate.html]

Whitmarsh J and Govindjee (1995) Photosynthesis. In: Encyclopedia of Applied Physics, vol. 13, pp. 513–532. Stuttgart: VCH Publishers. (Revised and modified version can be found at [http://www.life.uiuc.edu/govindjee/paper/gov.html] [http://www.life.uiuc.edu/govindjee/paper/gov.html].)

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Gilmore, Adam M(Apr 2001) Cell Membranes: Intracellular pH and Electrochemical Potential. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001266]