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