Oxidative Phosphorylation - JUdoctors...Oxidation and Phosphorylation are tightly coupled Control of...

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10/7/2012 1 Oxidative Phosphorylation Meta- bolism Lippincott or Marks basic medical biochemistry NADH + O 2 NAD + + H 2 O ΔG= -52.6 Kcal/mole ADP + Pi ATP + H 2 O The Rate ? Need Enzyme(s) to catalyze the reaction

Transcript of Oxidative Phosphorylation - JUdoctors...Oxidation and Phosphorylation are tightly coupled Control of...

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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

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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

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Electron Carrying Groups

• Flavin Mononucliotide• Iron Sulfur Centers• Coenzyme Q• Cytochromes• Cupper

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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

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very long isoprenoid side chain Can accept one or two electrons

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Cytochromes (Heme-containing proteins)

Pyrrole

Light absorptionIron alternates between 3+ and 2+

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- Three classes of cytochromesa,b and c

- Distinguished by differences in their light-absorption- Each has different reduction potential

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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

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The Q cycle

QH2 2Fe-2S Cytochrome c1 cytochrome c

cyt bL

cyt bH

Q

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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

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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??

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Testing chemiosmotichypothesis

Bacteriorhodopsin

•Purple membrane protein from halobacter•Pumps proton when illumuminated

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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

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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

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Oxidation and Phosphorylation are tightly coupled

What if protons leak back into the matrix?Uncoupling

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Chemical uncouplers of oxidative phosphorylation

• Lipid soluble compounds • Rapidly transport protons across membrane

HA A- + H+

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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

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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)