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Rotational Catalysis Mechanism

Rotational Catalysis Mechanism. Binding-change model of b subunit Proton passage through F o  conformational change in b subunits Rotation of the cylinder of c & g subunits Every rotation of 120 o ; g contacts with a different b subunit  induce conformational change

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Rotational Catalysis Mechanism

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  1. Rotational Catalysis Mechanism • Binding-change model of b subunit • Proton passage through Fo  conformational change in b subunits • Rotation of the cylinder of c & g subunits • Everyrotation of 120o ; g contacts with a different b subunit  induce conformational change  b-empty conformation • Neighbors of b-empty : b-ADP or b- ATP • One complete rotation of g subunits ; Cycle of b-ADP b- ATP  b-empty  3 ATP synthesis • Opposite rotation of g subunit in a single F1 • ATP hydrolysis

  2. Detection of the Rotation of g SubunitH. Noji et al., 1997, Nature • Biotinylation and fluorescent label of actin • Assembly of g subunit and actin by streptavidin • 4 binding sites for biotin • Detection g subunit rotation under a fluorescence microscope in the presence of ATP

  3. Stoichiometries of O2 Consumption and ATP Synthesis • xADP + xPi+1/2O2 + H+ + NADH  xATP + H2O + NAD+ • X : P/O ratio or P/2e- ratio • Before the chemiosmotic model • P/O is an integer • 3 for NADH and 2 for succinate • After the chemiosmotic model • No requirement for P/O to be integer • 2.5 for NADH and 1.5 for succinate • Proton efflux : 10 for NADH, 6 for succinate • 4 protons for 1 ATP synthesis

  4. The proton-motive force for active transport • Adenine nucleotide translocase • Antiporter • Transport ADP inside & ATP out side ( 4 - charges out & 3 + charges in)  by transmembrane electrochemical gradient (pmf) • Phosphate translocase • Symporter • H2PO4 & H+ • Favored bytransmembrane proton gradient • ATP synthasome • ATP synthase + both translocases

  5. NADH Shuttle Systems from Cytosol to Mitochondria • Malate-aspartate shuttle • Liver, kidney, heart • 2.5ATP/1NADH

  6. NADH Shuttle Systems from Cytosol to Mitochondria • Glycerol 3-phosphate shuttle • Skeletal muscle and brain • Electron transfer to Q  Complex III • 1.5 ATP/ 1 NADH

  7. 19.3 Regulation of oxidative phosphorylation

  8. Regulation of Oxidative Phosphorylation • Acceptor control of respiration • ADP (as a Pi acceptor) • Mass-action ratio • [ATP]/ ([ADP][Pi]); Normally high • Inhibitory protein • IF1 : bind to two ATPases as a dimer • Inhibition of ATP hydrolysis during hypoxic conditions (heart attack or stroke) • Dimerization is favored at low pH • Oxygen limitation fermentation  lowering pH

  9. Hypoxia Condition favorable for ROS generation • Defense systems in Mito • SOD & Glutathione peroxidase • Regulation of PDH by PDH kinase • Replacement of one subunit of complex IV (COX4-1 COX4-2)

  10. ATP-Producing Pathways are Coordinately Regulated Ratio of [ATP]/[ADP]  Coordinated regulation of major catabolic pathways

  11. 19.4 Mitochondria in thermogenesis, steroid synthesis, and apoptosis • Other important functions of mitochondria • Heat generation • Steroid hormone synthesis • Apoptosis

  12. Heat generation by uncoupled mitochondria • Thermogenin (uncoupling protein) • Unique protein in the mitochondria of brown adipocytes • (brown adipose tissue; BAT) • Path for H+ to matrix • Oxidation energy  Heat dissipation •  Body temperature maintenance • Newborn mammals and hibernating animals

  13. Mitochondrial P-450 Oxygenase • Mitochondria is a site for steroid H production • ; sex H, glucocorticoids, mineralocorticoids, Vit D H • Adrenal glands & gonads • Mitochondrial cytochrome P-450 • Heme containing enz • Serial hydroxylation of cholesterol or related sterol • R-H + O2 + NADPH  R-OH + H2O + NADP+ • Dozens of cyt P-450 located in the inner mito membrane • Complex e- flow from NADPH to P-450 heme • ER cytochrome P-450 in hepatocytes • Similar catalytic mechanism as mito cyt P-450 • Hydroxylation of xenobiotics clearance through kidneys

  14. Initiation of apoptosis • Apoptosis (programmed cell death) • Critical during embryonic development • Conservation of cell’s molecular components • Triggered by external death signals or internal events (DNA damage, viral infection, ROS, stresses) • Mitochondrial cyt C

  15. 19.5 Mitochondrial Genes: Their Origin and the Effects of Mutations

  16. Mitochondrial Genome • Circular, double stranded DNA • ~ 5 copies of the genome in each mitochondria • Human mitochondrial chromosome • 37 genes (16,569 bp)  13 genes for proteins in respiratory chain  Genes for rRNA, tRNA for protein-synthesizing machinery

  17. Origin of mitochondria • Hypothesis of endosymbiotic origin • mt DNA, ribosomes, tRNAs • Enzymatic machinery for oxidative phosphorylation • FoF1 complexes “Mitochondria is originated from endosymbiotic bacteria in primitive eukaryotes” • Respiration-linked H+ extrusion (pmf) • Nutrient symport with H+ (lactose) • Rotatory motion of bacterial flagella

  18. Mutations in mt DNA • Accumulation of mt DNA mutation throughout the life • Major site for ROS • Ineffective systems for mistake correction during replication • & Ineffective DNA-damage repair systems • Variation among individual cells in one organism • & variation among organism

  19. Photosynthesis: Harvesting light energy CO2 + H2OlightO2 + (CH2O)

  20. 19.6 General features of photophosphorylation

  21. Photosynthesis in plants • Two processes • Light reaction • - light energy  ATP & NADPH, • - O2 release from • Carbon-assimilation reations (carbon-fixation) • - CO2 carbohydrate; using ATP & NADPH

  22. Chloroplasts • The light-dependent & the carbon-assimilation reactions • Outer & inner membranes • Thylakoids (arranged in stacks ‘grana’) • ; its membrane embedding • - Photosynthetic pigments • - Enzyme complexes for light reactions & ATP synthesis • Stroma • - Enzymes for carbon-assimilation reactions

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