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Celi Membranes: Intracellular pH and Electrochemical Potential

Membranę

Figurę 1 Principles of the chemiosmotk hypothesis. (a) The electron and proton carriers are shown arranged vectorially across the energy-transducing membranę, (b) Coupied vectońal electron transport and/or ATP hydrolysisby the F -ATPasedeposit protons on the p-side of the ve*lde to inerease the pmf. ATP synthesis is driven forward when protons are conducted through the F₀ from the p-side to F ₍ on the n-side. Uncoupierś equilibrate protons and/or hydroxyt ions across the membranę and dissipate the pmf.

Ftgure 2 Typical eukaryotic mitochondrion and chloroplast. The mitochondrion (a) is shown with an enlarged view of the inner membranę and associated respiratory energy-transducing components. The chloroplast (b) is shown with enlarged view of thylakoid membranę and associated photosynthetic energy-transducing components. FSP, Ricske iron su Bur protein; PSI, photosystem I; OEC, oxygen-evolving complex PC, plastocyanin; FNR, ferredoxin:NADP reductase; PQ, ptastoguinone.

Cytochromc c carrics clcctrons to complcx IV whkh red u ccs oxygcn (O;) to water (H₂0). Complcxcs I. III and IV translocatc protons from the matrix to the intcrmcm-branc spacc. Undcr physiological conditions the main pmf componcnt is the causcd by proton cxtrusion from the niatrix. The F-ATPase synthesizes ATP in the matrix-cxposcd F| portion when protons are conductcd from the intcrmcmbranc spacc (p-side) to the matrix (n-sidc).

Plant mitochondria rcscmblc other cukaryotcs with two additions: (I) they oxidizc cxtcrnal NAD(P)H (on the

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tNCYCLOPtWAOF SCKNCES / C 2001 Naliłc Pubfcshing Group / wwwxh/wt