Chapter 18 Oxidative phosphorylation  the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH 2 to O 2 by a series of electron carriers  take place in mitochondria, the major source of ATP in aerobic organisms  the culmination of a series of energy transformations that are called cellular respiration or simple respiration (p. 503)  Electron-motive force  NADH-Q oxidoreductase, Q-cytochrome c oxidoreductase,  cytochrome c oxidase Proton-motive force  Phosphoryl transfer potential (ATP synthase)  Proton gradients are an interconvertible currency of free energy in biological systems

(oxidative phosphorylation) (TCA cycle, fatty acid oxidation) §18.1 Oxidative phosphorylation in eukaryotes takes place in mitochondria: 2  m in length and 0.5  m in diameter Kennedy and Lehninger quite permeable voltage-dependent anion channel (mitochondrial porin) Impermeable a large family of transporters shuttles metabolites matrix side (N side) cytosolic side (P side)

1M reduction potential of H + :H 2 couple = 0 §18.2 Oxidative phosphorylation depends on electron transfer Measurement of redox potential (E 0 ’ )  to evaluate electron-transfer potential (G° ’ )

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½ O 2 + NADH + H +  H 2 O + NAD +  G 0' = kcal mole -1 p. 508 Release energy is used 1. proton gradient formation  ATP synthesis ATP hydrolysis  G 0' = -7.3 kcal mole transport metabolites across the Mito. membrane H + matrix  cyto : 5.2 kcal mole -1  G°= -nF  E 0 faraday (23.05 kcal mol -1 V -1 ) △ G = RT ln(C 2 /C 1 ) + ZF △ V pH lower

§ 18.3 Four complexes in respiratory chain Electron affinity high Respirasome 1,2,3 1,2,4 ?

Nelson does not pump protons

N P

Respiratory chain complexes separation ATP synthase (complex V) In vitro, hydrolytic activity Nelson

Universal electron acceptors: NADH and NADPH: are water soluble, can’t cross inner Mito. membrane carry e - from catabolic rxs. vs. supply e - to anabolic rxs. [reduced form]/[oxidized form] hydride Nelson UV p. 499

Universal electron acceptors: Flavin nucleotides (FMN or FAD): are bound to flavoproteins which determine the reduction potential of a flavin nucleotide a part of the flavoprotein’s active site flavoproteins can participate in either one- or two- electron transfer Nelson

Universal electron acceptors: Ubiquinone (coenzyme Q, Q): a lipid-soluble molecule can accept one or two e - carry both e - and proton Nelson Q pool: a pool of Q and QH 2 exist in the inner Mito. membrane

Universal electron acceptors: iron-sulfur proteins: one-electron transfer non-heme iron proteins without releasing or binding protons 1 Fe — 4 Cys 2 Fe — 2 S — 4 Cys 4 Fe — 4 S — 4 Cys Rieske iron-sulfur proteins: 2 His residues replace 2 cys residues Nelson p. 511 Phosphorylation at His

Universal electron acceptors: cytochromes: a, b, c three classes in Mito. one-electron transfer The longest-wavelength 600 nm 560 nm 550 nm Covalently associated to proteins The standard reduction potential (p. 507) Nelson (C 17 ) Vinyl group

Reduced state (Fe 2+ )Nelson Color?

1. NADH-Q oxidoreductase (NADH dehydrogenase, complex Ⅰ ) NADH + Q + 5H + matrix  NAD+ + QH 2 + 4H + cytosol

Nelson 2. Succinate-Q reductase (complex Ⅱ ) p. 528

Q cycle: semiquinone radical anion

Nelson

3. Q-cytochrome c oxidoreductase (cytochrome bc1 complex; cytochrome reductase; complex Ⅲ ) His replace cys 1e - Q  3(hemes)  cytochrome c 1(2Fe-2S) during Q cycle

4 cyt c red + 8 H + N + O 2  4 cyt c ox + 2 H 2 O + 4 H + P 4. Complex Ⅳ : Cytochrome c oxidase e - from cytosol to O 2 2 heme a, 3 copper ions 3 subunits Cu A /Cu A  heme a  heme a 3  Cu B  O 2 ferric/ferrous cupric/cuprous ? Nelson

1 st e - Cupric (Cu 2+ )  Cuprous (Cu + ) 2 nd e - Ferric (Fe 3+ )  Ferrous (Fe 2+ ) 3 th and 4 th e -

Proton transport by complex Ⅳ 4 cyt c red + 8 H + N + O 2  4 cyt c ox + 2 H 2 O + 4 H + P  Charge neutrality and Conformational changes (p. 517)  G 0’ 4 H +  5.2 kcal/mole (p. 509)  2   0.82 (Tab. 18.1)

only electrons transfer, no protons transport NADH + 11 H + N + ½ O 2 → NAD H + p + H 2 O FADH 2 6

Reactive (active) oxygen species (R[A]OSs)  superoxide radical ( · O 2 - ), peroxide (O 2 2- ), hydrogen peroxide (H 2 O 2 ), hydroxyl radical (OH·), singlet oxygen (O 2 1 )  superoxide dismutase (SOD): Cu/Zn-; Mn-; Fe- catalase (CAT): 2 H 2 O 2  O 2 + 2H 2 O a heme protein peroxidase: H 2 O 2 + RH 2  2 H 2 O + R [ascorbate or glutathione peroxidase] SOD: 2 · O H +  O 2 + H 2 O 2 Dismutation: a reaction in which a single reactant is converted into two different products Antioxidant vitamins: Vit C: Vit E: lipophilic, avoid lipid peroxidation Danger lurks in the reduction of O 2

Radical · Q – from complex Ⅰ to QH 2 QH 2 to b L of complex III Also from pentose phosphate pathway Nelson p. 722

Type Ⅰ : insulin dep. a paucity of pancreatic  cells Type Ⅱ : non-insulin dep. slow to develop, in older, obese individuals insulin is produced, but some feature of the insulin-response system is defective The characteristic symptoms of both types: polydipsia, polyuria, glucosuria Aerobic metabolism   More ROS  More protective enzymes were induced