Metabolic Biochemistry BIBC102

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Metabolic BiochemistryBIBC102

• Lecture 14
• November 5, 2007

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LNC Fig.19.7
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the arrangement of the complexes in the inner
membrane and the order of electron flow
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Red the components are drained of electrons,
i.e. oxidized
Blue the components are filled with electrons,
i.e. reduced
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succinate
Succinate dehydrogenase membrane bound enzyme
of Krebs cycle
Four integral membrane protein complexes Two
mobile carriers ubiquinone and cytochrome c
LNC Fig.19.15
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oxidized Coenzyme Q or Q
reduced Coenzyme Q or QH2
LNC Fig.19.2
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What makes proteins conductors of electrons?
They get spiked with Fe ions Fe2/Fe3
Two kinds of structures Fe-S centers and hemes
Near the end of the chain we also encounter some
Cu ions
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Heme apoprotein cytochrome
LNC Fig.19.3
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Structure of cytochrome c
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LNC Fig.19.4
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NON-HEME IRON - SULFUR CENTERS Fe2-S2 Fe4 -
S4
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LNC Fig.19.5
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Fe2-S2
LNC Fig.19.5
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Fe4-S4
LNC Fig.19.5
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LNC Fig.19.5
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O2
NADH
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succinate
Succinate dehydrogenase membrane bound enzyme
of Krebs cycle
Four integral membrane protein complexes Two
mobile carriers ubiquinone and cytochrome c
LNC Fig.19.15
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7 or 8
NADH Q H ? NAD QH2
LNC Fig.19.9
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We have the crystal structure for
this subdomainof complex I from a bacterium
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NADH Q H ? NAD QH2
LNC Fig.19.9
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From Sazanov and Hinchliffe (2006) Science
3111430-1436
NADH
Q
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From Sazanov and Hinchliffe (2006) Science
3111430-1436
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Architecture of Succinate Dehydrogenase and
Reactive Oxygen Species Generation Victoria
Yankovskaya,1 Rob Horsefield,2 Susanna
Tornroth,3 Cesar Luna-Chavez,1,4 Hideto
Miyoshi,5 Christophe Leger,6 Bernadette Byrne,2
Gary Cecchini,1,4 So Iwata2,3,7 SCIENCE 31
JANUARY 2003 VOL 299, p.700 www.sciencemag.org
succinate
2Fe-2S 3Fe-4S 4Fe-4S
Succinate FAD ? fumarate FADH2FADH2
Q ? QH2 FAD __________________
________________ Succinate Q ? fumarate
QH2
Succinate Q ? fumarate QH2
LNC Fig.19.10
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Complex III 8-11 polypeptides two cytochromes, b
and c1 one iron-sulfur center
QH2 2 cyt c (Fe3) ? Q 2 cyt c
(Fe2) (ignore the protons for the moment)
LNC Fig.19-11
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LNC Fig.19-11b
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The Q Cycle
LNC Fig.19-12
Net equation QH2 2 cyt cox 2Hin ? Q 2
cyt cred 4Hout
2 Fe3
2 Fe2
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Cyt c1 red Cyt c ox ? Cyt c1 ox Cyt c
red
Fe3
Fe3
Fe2
Fe2
?
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Complex IV - cytochrome oxidase 9 - 13
polypeptides (not all shown here) cytochromes a
and a3 two copper centers
4 cyt c (Fe2) O2 4H ? 4 cyt c (Fe3)
2 H2O ( and protons pumped)
LNC Fig19-13a
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Complex IV (schematic)
4 cyt cred O2 4 H 4 cyt cox
2 H2O
Fe2
Fe3
LNC Fig.19-14
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Free Energy
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An excerpt from Table 13-7, in reverse order But
note there is a mistake in Table 13.7 for the
reduction of ubiquinone
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2 NADH 2 H O2 gt 2 NAD 2 H2O
NADH H 1/2O2 gt NAD H2O

• the half reactions
• NAD H 2e- ltgt NADH Eo '
  - 0.315 V
• 1/2 O2 2 H 2e- ltgt H2O Eo '
  0.815 V
• NADH 1/2O2 H ltgt H2O NAD
• DEo ' 0.815 0.315 1.130 V
• DEo ' Eo ' (electron acceptor) - Eo '
  (electron donor)
• DGo ' - n F DEo '
• where F is the Faraday constant 96,494 kJ/volt
  . mole, and substitution yields
• DGo ' - 2
  x 96,494 x 1.13 - 218 kJ/mole (NADH)
• since it takes 30.5 kJ/mole ATP to make ATP from
  ADP and Pi, we can in principle make 218/30 7
  moles ATP per NADH if a suitable coupling
  mechanism could be found and it worked at 100
  efficiency

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How is electron transport coupled to ATP
synthesis ?
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4H
2H
4H
IMS
MATRIX
LNC Fig.19.15
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Proton pumping and Storage of Free Energy
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IMS
Matrix
inner membrane
H
H
LNC 19-6
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DG 2.3 RT DpH 1 x F x DY
DpH 0.75 DY 0.15 - 0.2 v DG
20 kJ/mol (H)
The oxidation of NADH liberates 220 kJ/mol
(NADH) therefore, we can pump 11 protons at
100 efficiency
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tightly coupled vs uncoupled mitochondria
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succinate
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LNC 19-18a
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LNC Fig.19.8
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End of Lecture 14 February 9, 2007