2012 Electron Transport
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Transcript of 2012 Electron Transport
1
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