5.初級版課件4english vesion英文版-abridgedoxidation

1、Chapter20 Biological oxidationOutlineDefinitionComparison with Non-biological oxidation Electron transport chain or Respiratory chainOxidative phosphorylation (OxP)Inhibitors of ETC & OxPRespiratory control and P/O ratio (self-study)All oxidation reactions occurring in the living thingsCommon featur

2、es shared by Non-biological OxidationReaction nature is loss of electron or gain of oxygenRelease the same amount of energyUnique featuresMild reaction conditionsMany stepsInvolving a lot of enzymes and coenzymesBiological OxidationNAD+ and NAD+ -linked Dehydrogenases-NAD+ is a mobile electron carri

3、erFlavin and Flavin-linked DehydrogenasesCoQ（UQ）-also a mobile electron carrierIron-sulfur protein Cytochromes-Cyto c is a mobile electron carrier tooO2Components of ETCReduction of NAD+ to NADHReduction of FAD to FADH2Reduction of CoQ to CoQH2Iron-sulfur proteinsFe 3+ + e-Fe 2+Different heme groups

4、 found in different cytochromesMeasuring E0: Direction of electron flow is E01low E01high (energetically favorable)Spectra analysis: carriers closer to oxygen are more oxidized.Using Specific inhibitors & Artificial e-acceptorsDetachment & bination of Respiratory chain and Assay of individual comple

5、xes.Determining the order of electron carriersStandard Reaction Potentials of Respiratory Chain & Related Electron CarriersDetachment of Respiratory chain and Assay of individual complexesSequence of ETCElectron flow along the ETCElectron flow along the ETCCoupling e- Transport and Oxidative Phospho

6、rylationThis coupling was a mystery for many years The chemiosmotic hypothesis - Peter Mitchell proposed a novel idea - a proton gradient across the inner membrane could be used to drive ATP synthesis. Mitchell was ridiculed, but eventually won him a Nobel prize. The proton-motive force (pmf) is the

7、 sum of a transmembrane proton concentration (pH) gradient and electric potential Oxidative PhosphorylationThe coupling of electron transport and ATP synthesisProton Motive Force (pmf)F1/F0 ATP SynthaseProton diffusion through the protein drives ATP synthesis!Two parts: F1 and F0 (latter was origina

8、lly F-o for its inhibition by oligomycin) 1) F1 catalytic subunit, made of 5 polypeptides with stoichiometry a3b3gde. 2) Fo complex of integral membrane proteins that mediates proton transport. ab2c10 Racker & Stoeckenius confirmed Mitchells hypothesis using vesicles containing the ATP synthase and

9、bacteriorhodopsinATP Is Synthesized by the Binding Change Mechanism. The mechanism of ATP synthesis by proton-translocating ATP synthase can be conceptually broken down into three phases:Translocation of protons carried out by F0.Catalysis of formation of the phosphoanhydride bond of ATP carried out

10、 by F1.Coupling of the dissipation of the proton gradient with ATP synthesis, which requires interaction of F1 and F0.Proposed by Paul BoyerThe Binding Change MechanismThe Binding Change MechanismBinding change and rotational catalysisReaction Mechanism of F1F0-ATP SynthaseConsists of two complexes,

11、 F0, and F1.F0 unit is bound withinMembraneF1 is the catalytic Unit and consists ofa, b, g, d, e subunits.Proton flow C unit rotates g rotates conformation change ATP synthesizedMatrix SideThe proton gradient drives the release of ATP from the enzyme surfaceATP is stabilized by binding to enzyme. Fr

12、ee energy required for its release is provided by proton-motive force. Inhibitors of Oxidative PhosphorylationRotenone inhibits Complex I - and helps natives of the Amazon rain forest catch fish! AmytalAntimycin ACyanide, azide and CO inhibit Complex IV, binding tightly to the ferric form (Fe3+) of

13、a3 Oligomycin and DCCD are ATP synthase inhibitorsSome Agents that interfere with OxP Inhibitors of Oxidative PhosphorylationUncouplers and Uncoupling proteinUncoupling e- transport and oxidative phosphorylation Uncouplers disrupt the tight coupling between electron transport and oxidative phosphory

14、lation by dissipating the proton gradient Uncouplers are hydrophobic molecules with a dissociable proton They shuttle back and forth across the membrane, carrying protons to dissipate the gradient An uncoupling protein (thermogenin) is produced in brown adipose tissue of newborn mammals and hibernating mammals. This protein of the inner mitochondrial membrane functions as a H+carrie