Post on 19-Jan-2021
10/7/2012
1
Oxidative PhosphorylationMeta-bolism
Lippincott orMarks basic medical biochemistry
NADH + O2 NAD+ + H2O ΔG= -52.6 Kcal/mole
ADP + Pi ATP + H2O
The Rate ?
Need Enzyme(s) to catalyze the reaction
10/7/2012
2
NADH-QOxidoreductase
Q-Cytochrome C Oxidoreductase
Cytochrome C Oxidase
Coenzyme Q
Cytochrom C
NADH
O2
Complex I
Complex IV
Complex III
Inner mitochondrial membrane
Impermeable to most ions, small and large molecules
MatrixEnzymes of TCA
Cycle, Fatty acid and amino acid oxidation
10/7/2012
3
Electron Carrying Groups
• Flavin Mononucliotide• Iron Sulfur Centers• Coenzyme Q• Cytochromes• Cupper
10/7/2012
4
Flavin Mononucliotide( FMN)
• Can accept one or two electrons •Tightly bound to protein• Reduction potential: affected by interaction with protein
Iron Sulfur CentersThree TypesInorganic Sulfur Coordinated to Cysteine sulfur
10/7/2012
5
very long isoprenoid side chain Can accept one or two electrons
3
2
Cytochromes (Heme-containing proteins)
Pyrrole
Light absorptionIron alternates between 3+ and 2+
10/7/2012
6
- Three classes of cytochromesa,b and c
- Distinguished by differences in their light-absorption- Each has different reduction potential
10/7/2012
7
Complex I:-NADH Dehydrogenase-A huge flavoprotein complex.- Membrane- Spanning. - More than 25 polypeptide chain- Tightly bound FMN group-Seven Fe-S centers of at least two different types- Drop in energy≈ -13 to 14 kcal
Q-cytochrome c Oxidoreductase(Cytochrome reductase or cytochrome bc1)• Catalyzes the transfer of electrons from QH2 to
cytochrome c• 11 subunits including two cytochrome subunits • Contain iron sulfur center• Contain three heme groups in two cytochrome
subunits– bL and bH in cytochrome b– c type in cytochrome c1
• Contain two CoQ binding sites
10/7/2012
8
The Q cycle
QH2 2Fe-2S Cytochrome c1 cytochrome c
cyt bL
cyt bH
Q
10/7/2012
9
Passes electrons from Cytocrome c to oxygen• Contains cytochrome a and a3• Contains two copper• Contains oxygen binding sites• O2 must accept 4 electrons to be reduced to two H2O• Cytochrome c is one electron carrier
Cyt cred + 4H+ + O2 → Cyt cox + 2H2O• Partial reduction of O2 is hazardous.
Cytochrome Oxidase
10/7/2012
10
10/7/2012
11
10/7/2012
12
In the absence of oxygen, electron flow stops
Blocking by any of the inhibitors stops the flow of electron from substrate to oxygen
Reduced or oxidized state??
10/7/2012
13
Testing chemiosmotichypothesis
Bacteriorhodopsin
•Purple membrane protein from halobacter•Pumps proton when illumuminated
10/7/2012
14
ATP synthase• Large multisubunit enzyme
complex• Originally (mitochondrial
ATP’ase) FOF1 ATP’ase• FO Transmembrane: Proton
channel, 12 c and 1 a subunits
• F1 Head piece 3α3βγδε• F1 catalytic activity
The proton channel depends on both the a subunit and the c ring
The F0 and F1 subunits are connected in two ways:- central γϵ stalk- an exterior column
Αβ dimers have three different conformationsT tightL looseO open
10/7/2012
15
Oxidation and Phosphorylation are tightly coupled
Control of oxidative phosphorylation
Control of oxidative phosphorylation• Electrons do not flow through electron
transport chain to O2 unlessADP ATP
• Oxidative phosphorylation requires:Source of electrons (NADH or succinate)ADP, Pi, O2
Respiratory control
10/7/2012
16
Oxidation and Phosphorylation are tightly coupled
What if protons leak back into the matrix?Uncoupling
10/7/2012
17
Chemical uncouplers of oxidative phosphorylation
• Lipid soluble compounds • Rapidly transport protons across membrane
HA A- + H+
•
10/7/2012
18
Uncoupling proteins and thermogenesis• Form channels through the membrane and • Cconduct protons from intermembrane space
to matrix– UCP1 Thermogenin in brown adipose tissue– UCP2 , UCP3 , UCP4 , UCP5 in other tissues
10/7/2012
19
10/7/2012
20
OxPhos Diseases• DNA in mitochondria mtDNA encodes 13 subunits
of comlexes I, III and IV• High rate of mutations (10x nuclear DNA)• Muta ons → Defect in oxida ve phosphorylation.
– Tissues with highest ATP demands affected most• Maternal inheritance• Accumulation of somatic mutations with age• Examples:- Leber's hereditary optic neuropathy
-myoclonic epilepsy and ragged-red fiber disease (MERRF)