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Electron Transport and

Oxidative Phosphorylation

General Biochemistry

2012

Glucose Oxidation (Glycogen)

1.Phase – glycolysis (glycogenolysis)

2.Phase – citric acid cycle

3.Phase – electron transport and oxidative phosphorylation

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Electron Transport

Localization: inner mitoch. membrane Cristae – the density of cristae is related to

the respiratory activity of a cell

Energy: the oxidation of NADH and FADH2 will produce most of the ATP generated by the oxidation of Glc

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Mitochondrion

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The Electron Transport Chain

Complex I (NADH-coenzyme Q reductase)

FMN (1x)

Fe-S centers (6-7x)

Complex II (succinate-coenzyme Q reductase)

Succinate dehydrogenase (1xdimer), FAD (2x)

Fe-S centers (9x)

Cyt b560

The Electron Transport Chain

Complex III (coenzyme Q-cyt c reductase)

Cyt b (2x)

Fe-S centers (1x)

Cyt c1 (1x)

Complex IV (cyt c oxidase)

Cyt a

Cu (2x)

Cyt a3

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Complex I

The largest enzyme of inner mitochondrial membrane, 26 subunits (850 kDa)

NADH – FMN – Fe-S – CoQ

-0,32 -0,30 +0,04

FMN

All forms are stable

Ability to accept or donate 1 or 2 e-

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Fe-S centers

Fe in each center forms conjugative system (+2; +3)

Coenzyme Q

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Complex II

5 subunits = dimer of succinate dehydrogenase, 3 other small hydrophobic subunits, (127 kDa)

succinate – FAD – Fe-S – cyt b560 – CoQ

+0,030 -0,040 -0,080 +0,045

it is not proton pump because the free-energy change of the catalyzed reaction is too small

important for electron enter (with relatively high potential) into the electron transport chain

FAD

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Complex III

10 subunits, (280 kDa)

CoQ – cyt b562 – cyt b566 – Fe-S – cyt c1 – cyt c

+0,045 +0,030 -0,030 +0,215 +0,235

Cytochromes: Hem Proteins

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Cytochromes: Hem Proteins

Cytochrome c

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Complex IV

Dimer protein, 6-13 subunits, (160-200 kDa)

cyt c – cyt a – CuA – CuB – cyt a3 – O2

+0,235 +0,210 +0,245 +0,340 +0,385 +0,815

4 cyt c2+ + 4H+ + O2 4 cyt c3+ + 2H2O

Complex IV – Electron Transport

FeII-O-O-CuI

FeIII-O--O--CuII

FeII-OH-O--CuII

FeIV=O + -HO-CuII

FeIII-OH- + -HO-CuII

2H2O + FeIII + CuII

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Q Cycle

Redox Potential Changes

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1978 – Peter D. Mitchell Nobel Prize for Chemistry

Complex V

ATP-synthase

2 subunits

Generation of a proton gradient permits ATP synthesis

Changes by H+ translocation

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ATP Synthesis

F1 unit has 3 catalytic b subunits, which are intrinsically identical but are not functionally equivalent at any particular moment L=loose – binds the substrates loosely and is catalycally inactive

T=tight – binds them tightly and is active

O=open – has very low affinity for substrates

1997 – (Paul D. Boyer, John E. Walker, Jens C. Skou) Nobel Prize for Chemistry

Uncoupling of Oxidative Phosphorylation

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Respiratory Control

Control by substrate availability

ADP, Pi, O2, NAD+, FAD+

Cytochrome oxidase Regulatory enzyme

Control by substrate availability – reduce form of cyt c (c 2+ )

[c2+]/[c3+] = ([NADH]/[NAD+]) x ([ADP][Pi]/[ATP])

Regulation by acceptor – regulaion by ATP/ADP