Oxidative PhosphorylationWhat is it?

Process in which ATP is formed as a result of the transfer ofelectrons from NADH or FADH2 to O2 via a series of electron carriers

Oxidation of glucose:Glycolysis: 2ATP 2NADH (5ATP)Pyruvate dehyd: 2NADH (5ATP)Citric acid cycle: 2ATP 6NADH (15ATP) 2FADH2 (3ATP)Oxidative phos: ~26-28ATP

TOTAL: ~30-32ATP

K, lec18, p2

Occurs in mitochondria

Oxidative PhosphorylationWhat is mitochondria?2 membranes:Inner - only permeable to O2, H2O transporters req’d for ATP, Pi, pyruvate, etc. folding increases surface area (site of ox. phos. machinery)Matrix contains:citric acid cycle enzymesFatty acid oxidation enzymes (discuss later)

Oxidative PhosphorylationSummary

F type transporterATP synthase

Oxidative PhosphorylationHistory

1961 - Peter Mitchell proposed chemiosmotic hypothesis: energyfrom e- transport is stored in a proton gradient which is then used tomake ATP

Experimental support:1. Uncouplers: dinitrophenol carries H+ across membrane,dissipating the H+ gradient

DNP-treated mito endlessly consume O2 with NO ATP synthesis

2. Artificial H+ gradients drive ATP synthesis

K, lec18, p16

K, lec18, p17

Oxidative PhosphorylationWhat are the electron carriers?

NADH, NADPH (cannot cross inner mito membrane, shuttle their e-)FMN, FAD (directly involved in Ox phos)

NADH, NADPH and FADH2 each carry 2e-

FMN can carry 1 or 2e-

Membrane boundHydrophobic quinone (coenzyme Q)Q can carry 1 or 2e- Q floats free in lipid bilayer and ferries e- from complexes I and II to III

Oxidative Phosphorylation

Iron-containing proteins (cytochromes and Fe-S proteins)Cyt carry 1 e-, heme, found in complexes III and IV and cytochrome c

Oxidative Phosphorylation

FeS carry 1 e-, found in complexes I, II, and III, Fe2+ or Fe3+

Cytochrome cPeripheral membrane protein that shuttles e- between complexesIII and IVFe is linked to His and Met side chains

Oxidative Phosphorylation

K, lec 18, p11

Oxidative Phosphorylation

Electron transport chain (respiratory chain)Series of oxidation/reduction components that carry electrons

Complex I(NADH-Q dehydrogenase)

Complex II(Succinate-Q dehydrogenase)

Coenzyme Q

Complex III(Cytochrome reductase)

Cytochrome c

Complex IV(cytochrome oxidase)

FMN, FeS

FAD, FeS

itself

Cyt bH, Cyt bL, FeS, Cyt c1

itself

Cyt a, Cyt a3, CuA, CuB

Protein e- carrying components

Oxidative PhosphorylationOrder of electron carriers determined by respiratory inhibitors

NADH → FMN → FeS → Q → cyt b → FeS → cyt c1 → cyt c → cyt a → cyt a3 → O2

rotenone antimycin A cyanide, azide

Oxidative Phosphorylation

Complex I: NADH:Ubiquinone oxidoreductaseNADH to Q

(Proton pump)

Oxidative Phosphorylation

Complex II: Succinate dehydrogenaseSuccinate to Q

QH2

Oxidative Phosphorylation

Complex III: Cytochrome bc1 complex or ubiquinone:cytochrome coxidoreductaseUbiquinol (QH2) to cytocrome c

Oxidative Phosphorylation

Complex IV: Cytochrome oxidaseCytocrome c to molecular O2 (reducing it to H2�O)

Oxidative Phosphorylation

ATP synthaseMultiprotein complex3H+ pass through for each ATP made

K, lec18, p18

OUTER MEMBRANE

Oxidative PhosphorylationEnergetics of Ox. Phos.

1/2 O2 + NADH + H+ ⇔ H2O + NAD+

ΔG˚ = -220 kJ/mol

An electrochemical gradient across the inner membrane is formed:electrical: outside is more positivechemical: proton concentration gradient (pHout is 1.4 units < pHin

Energy of 3H+ transported drives ATP synthesis

ADP + Pi + 3H+ ⇔ ATP + H2OΔG˚ = +30.5 kJ/mol

Oxidative PhosphorylationControlOx. Phos cannot occur without:

source of e- (NADH)sink for e- (O2)substrates for ATP synthase (ADP and Pi)

[ADP] is limiting factor

Oxidative PhosphorylationHow does ATP made in mito get out?