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Chapter 18 Oxidative phosphorylation the process in which ATP is formed as a result of the transfer of
electrons from NADH or FADH2 to O2 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 permeablevoltage-dependent anion channel (mitochondrial porin)
Impermeablea large family of transporters shuttles metabolites matrix side (N side) cytosolic side (P side)
1M reduction potential of H+:H2 couple = 0
§18.2 Oxidative phosphorylation depends on electron transfer
Measurement of redox potential (E0’)
to evaluate electron-transfer potential (G°’)
½ O2 + NADH + H+ H2O + NAD+
G0' = - 52.6 kcal mole-1 p. 508
Release energy is used
1. proton gradient formation ATP synthesis
ATP hydrolysis G0' = -7.3 kcal mole-1
2. transport metabolites across the Mito. membrane H+
matrix cyto: 5.2 kcal mole-1
G°= -nF E0 faraday (23.05 kcal mol-1V-1)
△ G = RT ln(C2/C1) + 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 QH2
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
(C17)
Vinyl group
Reduced state (Fe2+) Nelson
Color?
1. NADH-Q oxidoreductase (NADH dehydrogenase, complex )Ⅰ
NADH + Q + 5H+matrix NAD+ + QH2 + 4H+
cytosol
Nelson2. 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-
1e-
Q 3(hemes)cytochrome c 1(2Fe-2S) during Q cycle
4 cyt cred + 8 H+N + O2
4 cyt cox + 2 H2O + 4 H+P
4. Complex : Cytochrome c oxidase Ⅳ
e- from cytosol to O2
2 heme a, 3 copper ions
3 subunits
CuA/CuA heme a
heme a3 CuB O2
ferric/ferrous cupric/cuprous
?Nelson
1st e-
Cupric (Cu2+)
Cuprous (Cu+)
2nd e-
Ferric (Fe3+)
Ferrous (Fe2+) 3th and 4th e-
Proton transport by complex Ⅳ4 cyt cred + 8 H+
N + O2 4 cyt cox + 2 H2O + 4 H+P
Charge neutrality and
Conformational changes
(p. 517)
G0’
4 H+ 5.2 kcal/mole (p. 509)
2 23.06 0.82
(Tab. 18.1)
only electrons transfer,
no protons transport
NADH + 11 H+N + ½ O2 → NAD+ + 10 H+
p + H2O
FADH2 6
Reactive (active) oxygen species (R[A]OSs)
superoxide radical (·O2-), peroxide (O2
2-), hydrogen peroxide (H2O2), hydroxyl radical (OH·), singlet oxygen (O2
1)
superoxide dismutase (SOD): Cu/Zn-; Mn-; Fe-
catalase (CAT): 2 H2O2 O2 + 2H2O a heme protein
peroxidase: H2O2 + RH2 2 H2O + R [ascorbate or glutathione peroxidase]
SOD: 2 ·O2- + 2H+ O2 + H2O2
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 O2
Radical ·Q– from complex Ⅰ to QH2
QH2 to bL of complex III
Also from pentose phosphate pathway
Nelson
p. 722
Type : insulin dep.Ⅰ
a paucity of pancreatic cells
Type : non-insulin dep.Ⅱ
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