Electron transport and oxidative phosphorylation...Electron transport and oxidative phosphorylation An experiment demonstrating that the ATP synthase is driven by proton flow. By

Electron transport and oxidative phosphorylation

Electron transport and oxidative phosphorylation

≈ 140 mV

≈ 60 mV

≈ 200 mV ≈ kBT pro H+

Electron transport in mitochondria is coupled to protontranslocation

Electron transport and oxidative phosphorylation

• Most of the free energy released during oxidation of glucose to CO2 is retained inNADH

• During respiration, electrons are released from NADH and eventually aretransferred to O2 (forming H2O)

• The step-by-step transfer of electrons via the electron transport chain allows thelarge amount of free energy produced by the transfer of electrons to O2 to bereleased in small increments

• Several electron transport chain components convert these small increments intoa proton and voltage gradient across the inner membrane

• The movement of protons down their electrochemical gradient drives thesynthesis of ATP from ADP and Pi

Electron transport and oxidative phosphorylation

≈ 800 kD22 proteins

≈ 500 kD8 proteins

≈ 300 kD9 proteins

The stepwise flow of electrons through the electrontransport chainThe redox potential increases aselectrons flow down the respiratorychain to oxygen. The standard free-energy change, for the transfer of thetwo electrons donated by an NADHmolecule can be obtained from theright-hand ordinate. Electrons flowthrough an enzyme complex by passingin sequence to the four or more electroncarriers in each complex. As indicated,part of the favorable free-energy changeis harnessed by each enzyme complexto pump H+ across the mitochondrialinner membrane. Although the numberof H+pumped per electron (n) isuncertain, it is estimated that theNADH dehydrogenase and b-c1complexes each pump two H+ perelectron, whereas the cytochromeoxidase complex pumps one.The twoelectrons transported from FADH2,generated by fatty acid oxidation and bythe citric acid cycle (see Figure 14-14),are passed directly to ubiquinone, andthey therefore cause less H+ pumpingthan the two electrons transported fromNADH (not shown).

The pathway of electron transport and proton transport inthe inner mitochondrial membrane

3 independent complexes with mobile carriers

The proton-motive Q cycle

Three-dimensional structures of some iron-sulfur clusters in electron-transporting proteins

Heme prosthetic groups of respiratory- chain cytochromesin mitochondria

Fe II <--> FeIII

Cytochrome C

Heme group

Coenzyme Q is theonly electron carrierthat is not a protein-bound prostheticgroup

The multiprotein complexes and associated prostheticgroups of the mitochondrial electron transport chain

Coupling of H+ pumpingand O2 reduction bycytochrome c oxidase

Molecular structure of the core of cytochrome c oxidase

Molecular structure of thecore of cytochrome c oxidase

Oxidation of reduced cytochrome c by cytochrome coxidase is coupled to proton transport

Electron transport and oxidative phosphorylation

Localizing and Manipulating Individual Bactriorhodopsins in a Purple Membrane

Oesterhelt, F.; Oesterhelt, D.; Pfeiffer, M.; Engel, A.; Gaub, H. E.; Müller, D. J. Science 2000, 288, 143-

Experiments withmembrane vesicles supportthe chemiosmoticmechanism of ATPformation

ATP synthase comprises aproton channel (F0) andATPase (F1)

Electron transport and oxidative phosphorylation

An experiment demonstratingthat the ATP synthase is drivenby proton flow. By combining alight-driven bacterialprotonpump (bacteriorhodopsin), anATP synthase purified from oxheart mitochondria, andphospholipids, vesicles wereproduced that synthesizedATP in response to light.

Mitochondrial F1 particles are required for ATP synthesisbut not for electron transport

Demonstration that the γsubunit of F0 rotatesrelative to the (αβ)3hexamer in an energy-requiring step

The F0F1 complex harnesses the proton-motive force topower ATP synthesis

Transporters in theinner mitochondrialmembrane are poweredby the proton-motiveforce

Rate of mitochondrialoxidation depends on ADP levels =respiratory control

Cytosolic enzymes convert glucose to pyruvate (steps 1-3)

The ATP Synthase can work reverse

Beispiel:Michaelis-MentenKinetik der F1-Atpase

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Beispiele von Reaktionszyklen mit kraftabhängigen Raten

ca. 50% Effizienz