Overview of the respiratory chain © Michael Palmer 2014

Functional stages in the respiratory chain 1.H 2 is abstracted from NADH+H + and from FADH 2 2.The electrons obtained with the hydrogen are passed down a cascade of carrier molecules located in complexes I–IV, then transferred to O 2 3.Powered by electron transport, complexes I, III, and IV expel protons across the inner mitochondrial membrane 4.The expelled protons reenter the mitochondrion through ATP synthase, driving ATP synthesis

Uncoupling proteins dissipate the proton gradient © Michael Palmer 2014

The uncoupling action of dinitrophenol © Michael Palmer 2014

The Racker experiment: bacteriorhodopsin can drive ATP synthase © Michael Palmer 2014

Molecules in the electron transport chain © Michael Palmer 2014

Iron-containing redox cofactors © Michael Palmer 2014

Flavin-containing redox cofactors © Michael Palmer 2014

The respiratory chain produces reactive oxygen species as byproducts © Michael Palmer 2014

Redox reactions can be compartmentalized to produce a measurable voltage © Michael Palmer 2014

The redox potential (ΔE) is proportional to the free energy (ΔG) © Michael Palmer 2014

Redox potentials and free energies in the respiratory chain © Michael Palmer 2014

The first two redox steps in complex I © Michael Palmer 2014

The reduction of coenzyme Q involves protons and electrons © Michael Palmer 2014

The Q cycle (criminally simplified) © Michael Palmer 2014

Reduction of oxygen by cytochrome C oxidase (complex IV) © Michael Palmer 2014

How is electron transport linked to proton pumping? ● Some redox steps in the ETC are coupled to proton binding and dissociation, which may occur at opposite sides of the membrane. Example: Coenzyme Q cycle at complex III ● Redox steps that do not involve hydrogen directly need a different mechanism in order to contribute to proton pumping. Example: Sequence of iron-sulfur clusters and hemes in complex IV

Linking electron movement to proton pumping: A conceptual model © Michael Palmer 2014

Proton pumping creates both a concentration gradient and a membrane potential © Michael Palmer 2014

Structure of ATP synthase © Michael Palmer 2014

The binding-change model of ATP synthase catalysis © Michael Palmer 2014

How does proton flux drive ATP synthase? © Michael Palmer 2014

Proton flux causes c chains to rotate within the F 0 disk © Michael Palmer 2014

A hypothetical malate-oxaloacetate shuttle © Michael Palmer 2014

The malate-aspartate shuttle © Michael Palmer 2014

The glycerophosphate shuttle © Michael Palmer 2014

The two mitochondrial isocitrate dehydrogenases © Michael Palmer 2014

Nicotinamide nucleotide transhydrogenase couples hydrogen transfer with proton transport © Michael Palmer 2014

At rest, transhydrogenase and the isocitrate dehydrogenases form a futile cycle © Michael Palmer 2014

When ATP demand is high, transhydrogenase turns into an auxiliary proton pump © Michael Palmer 2014

Theoretical ATP per molecule of glucose completely oxidized © Michael Palmer 2014

Processes other than ATP synthesis that are powered by the proton gradient ● Nicotinamide nucleotide transhydrogenase ● Uncoupling proteins; proton leak ● Secondary active transport: ○ ATP 4− /ADP 3− antiport ○ phosphate/H + symport ○ amino acid/H + symport ○ pyruvate/H + symport