1 / 22

Mitochondrial Function

Mitochondrial Function. Structure Citric acid cycle Electron transport Regulatory/modulatory signaling. Mitochondrial Structure. Principal metabolic engine Symbiotic bacteria 6k-370kBP genome Human: 13 proteins Dual membrane ie : two bilayers Outer membrane highly permeable

saniya
Download Presentation

Mitochondrial Function

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mitochondrial Function • Structure • Citric acid cycle • Electron transport • Regulatory/modulatory signaling

  2. Mitochondrial Structure • Principal metabolic engine • Symbiotic bacteria • 6k-370kBP genome • Human: 13 proteins • Dual membrane • ie: two bilayers • Outer membrane highly permeable • Inner membrane highly impermeable

  3. Mitochondrial Matrix • Highly oxidative environment • Unique proton gradient • High pH (8), negative (-180 mV), ~18 kJ/mole • H+ actively transported out of matrix • H+ leak back as H+PO4 2- • Capture gradient energy for ATP synthesis • H+ ATPase pump • ADP-ATP antiporter • Other proton co-transporters • Pyruvate, citrate • Glutamate, citruline

  4. CH3 C=O COO- Metabolic Substrates • Sugars • Metabolized in cytoplasm to pyruvate • Co-transported to matrix with H+ • Bound to Coenzyme A as Acetyl-CoA • Fatty acids • To intermembrane space as Acyl-CoA • To matrix as Acyl-carnitine • Metabolized to Acetyl-CoA in matrix • Proteins

  5. Acetyl Coenzyme A • Common substrate for oxidative metabolism • S-linked acetate carrier

  6. The Citric Acid Cycle Acetyl-Coenzyme A CoA These carbons will be removed NADH New carbons Oxaloacetate Citrate Carbon Malate Oxygen Isocitrate Coenzyme A NADH + = Fumarate a -Ketoglutarate FADH 2 Succinate Succinyl CoA CoA NADH + GTP CoA

  7. NAD+ + H++2e- NADH DE0=-0.32V ½O2+2 H++ 2e- H2O DE0=0.82V NADH + H+ + ½ O2 NAD+ +H2O Electron transport • Couple NADH/FADH2 electrons to H+ export • Ideally this completes • Electron leakage

  8. KEGG pathway • Enzyme Commission (EC) number • Hierarchical • Function-centric nomenclature • Compare • Gene Ontology (GO) ID • Entrez RefSeq • UniProt ID Metabolite KEGG http://www.genome.jp/kegg/pathway.html

  9. NAD+ FAD NADH FADH2 Cyclic redox reactions Oxidized CoQ/ubiquinone Cyto-C3+ O2 dihydroubiquinone Cyto-C2+ H2O Reduced NAD+  NADH E0 = -0.32V FAD FADH2 E0 = -0.22V Ubuquinone E0 = 0.10V Cytochrome C E0 = 0.22V O2  H2O E0 = 0.82V

  10. NADH/Complex I • Nicotinamide adenine dinucleotide • H dissociates as H- • Complex I (NADH reductase) • Then e- to ubiquinone • 46 subunit protein • Nuclear-derived proteins • mtDNA-derived proteins • Transfer e- to ubiquinone • Shuttle 2 H+/e-

  11. FADH2/Complex II • Flavin Adenine Dinucleotide • H disrupts C-ring • Electron transfer flavoprotein • Complex II • Succinate reductase • Transfers 2H• from succinate to FAD • No H+ transport • ETF-ubiquinone oxidoreductase • Transfers 2H• from FADH2 to ubiquinone

  12. Complex III and IV • Ubiquinone (UQ) • 2 electron carrier • Complex III (cytochrome reductase) • Transfer e- from ubiquinone to cytochrome c • Coupled with H+ transport • Rieske “2Fe2S” redox center • 1 Ub to 2 CyC http://bcs.whfreeman.com/stryer/pages/bcs-main.asp?s=00010&n=99000&i=99010.01&v=category&o=&ns=0&uid=0&rau=0

  13. Complex IV • Cytochrome oxidase • Transfer 1x e- from cytochrome C to oxygen • Coupled with H+ transport • 4x cytochrome yield 2xH2O • Transport complex • Supercomplex of I, III, IV • Stoichiometry of 1:2:4 • Transport 8 e- and 36 H+ per citrate • ATP?

  14. Mitochondrial membrane potential • Few ion channels • Low H+ • High H+ flux/H+ current • Proton equilibrium potential dominates membrane potential • DY ~ -100 mV relative to cytoplasm • H+ coupled transport • Malate, pyruvate, glutamate, Ca, Pi • Charge coupled transport • ATP:ADP exchange, Ca

  15. Proton ATPase/Complex V • ATP driven proton pump • “Reversible” • Couples H+ gradient to ATP synthesis

  16. Mitochondrial control • Mitochodrial nucleotide flux • Steady state (at rest), not equilibrium • Dynamic control • Membrane potential • Substrate+O2+ADPCO2+H2O+ATP ADP State 2 State 5 State 4Rest O2 CO2 Substrate (Glucose,pyruvate, NADH) H2O ATP

  17. Mitochondrial uncoupling poison NADH content Mitochondrial Depolarization Control by mitochondrial potential • NADH oxidation coupled to H+ transport • Greater Y, greater resistance, slower ox Leyssens et al., 1997

  18. Extreme mitochondria redox states • Substrate+O2+ADPCO2+H2O+ATP • State 1: substrate & ADP limited • State 2: substrate limited • State 3: enzyme limited • Maximal activity • State 4: ADP & Pi limited • Rest • State 5: O2 limited • <5-10 uM O2 ~ 15-30 mmHg, 2-4%

  19. Control by mitochondrial redox state • Cytochrome oxidase (complex IV) • Iron (heme) redox centers (Fe2+/Fe3+) • Copper redox center (Cu+/Cu2+) • Redox centers more oxidized • More O2 • Less ADP Fe State 3 Cu State 4 DE=DE0 - RT/nF ln(Qprod/Qreac) Redox cascade backs up by accumulation of product Hoshi, et al., 1993

  20. Extreme mitochondria redox states • State 1: substrate & ADP limited • Electron transport chain oxidized • High DY • State 2: substrate limited • ETC oxidized, low DY • State 3: enzyme limited • ETC reduced, low DY • State 4: ADP & Pi limited • ETC reduced, high DY • State 5: O2 limited • ETC reduced, high DY

  21. Control by calcium • Calcium activated enzymes • Pyruvate dehydrogenase • Oxoglutarate dehydrogenase • NAD+-isocitrate dehydrogenase • F0F1 • Membrane potential • Na-Ca antiporter • Ca uniporter  depolarization with cytoplasmic Ca • Reduce F0F1 efficiency • Increase NADH oxidation

  22. Electron leakage • Ubiquinone rapidly releases e- • Radical formation: O2• • Bypasses electron transport • Complex I • Complex III • Oxidative damage • Thiol crosslinking, DNA damage, etc • Inhibition of Complex I & III • Buffered by intermembrane GSH, Mn-SOD

More Related