Respirasomes Functional combination of two or more electron-transfer complexes Respirasome of complex III & IV Cardiolipin (abundant in inner mito membrane)  critical to formation of respirasomes

Conservation of the e - Transfer Energy in a Proton Gradient Standard free energy change of e - from NADH to O 2  NADH + H + + ½ O 2  NAD + + H 2 O   G ’o = -nF  E ’o = -220 kJ/mol  Oxidation of succinate   G ’o = -150 kJ/mol Using the energy to pump protons out of the matrix  4H + (complex I), 4H + (complex III), 2H + (complex IV) ; NADH + 11 H N + + 1/2O 2  NAD H p + + H 2 O

Conservation of the e - Transfer Energy in a Proton Gradient Electrochemcial energy  proton-motive force  Energy stored in proton gradient  Two components  Chemical potential energy : separation of chemical H +  Electrical potential energy : separation of charge

Proton-Motive Force Free energy change for the creation of electrochemical gradient by ion pump   G = RTln(C 2 / C 1 ) + ZF   C : concentrations of an ion, C 2 > C 1  Z : absolute value of electrical charge (1 for a proton)   transmembrane difference in electrical potential  ln(C 2 / C 1 ) = 2.3 (log [H + ] P - log [H + ] N ) = 2.3 (pH N – pH P ) = 2.3  pH   G = 2.3 RT  pH +F   Active mitochondria ;  0.15 ~ 0.2 V,  pH = 0.74   G = 19 kJ/mol (of H + )  ~ 200 kJ/mol (NADH)

Reactive oxygen species (ROS) ROS generation of oxidative phosphorylation - Radical Q - intermediate generated during complex I  QH 2 QH 2  complex III Pass an electron to O 2 O 2 + e -  O 2 - (superoxide) - Detoxification systems Superoxide dismutase (SOD) Glutathione peroxidase (GPx)

Oxidation of NADH in plant mitochondria Analogous to mito ATP synthesis mechanism of animal Plant specific alternative mechanism  Regeneration of NAD + from unneeded NADH  Direct e - transfer from ubiquinone to O 2 (bypassing complex III and complex IV)  Energy from e - transfer  heat generation  CN - alternative QH 2 oxidase

Oxidative Phosphorylation 19.2 ATP Synthesis

Chemiosmotic Model “ The electrochemical energy inherent in the difference in proton concentration and the separation of charge across the inner mitochondrial membrane – the proton-motive force – drives the synthesis of ATP as protons flow passively back into the matrix through a proton pore associated with ATP synthase” Chemical potential ∆ pH Electrical potential ∆ ψ

Coupling of Electron Transfer & ATP Synthesis Experiment to demonstrate ‘coupling’ ADP + P i succinate (1)Substrate oxidation (2)O 2 consumption (3)ATP synthesis Isolated mitochondria Experiment 1 (1)(ADP + Pi) addition  no respiration & ATP synthesis (2)Succinate addition  respiration & ATP synthesis (3)CN - addition  inhibiting respiration & ATP synthesis  Coupling of electron transfer & ATP synthesis

Coupling of Electron Transfer & ATP Synthesis Experiment 2 (1)Succinate addition  no respiration & ATP synthesis (2)(ADP + Pi) addition  respiration & ATP synthesis (3)Oligomycin or venturicidin addition  inhibiting respiration & ATP synthesis (4) DNP addition  continuing respiration without ATP synthesis (uncoupling)  Further demonstration of coupling of electron transfer & ATP synthesis

Chemical uncouplers  2,4-dinitrophenol (DNP) & carbonylcyanide-ρ- trifluoromethoxyphenylhydrazone (FCCP)  Weak acids with hydrophobic properties  Release protons in the matrix  dissipation of proton gradient  Ionophores  Valinomycin (peptide ionophore binding K + )  Transport of inorganic ions through membranes  dissipation of electrical gradient Coupling of Electron Transfer & ATP Synthesis

Evidence for the Role of a Proton Gradient in ATP Synthesis Artificial generation of electrochemical gradient  Leads to ATP synthesis without oxidizable substrate

Mechanism of ATP formation 1. Karl Lohman (1929) 2. Fritz Lipmann (1953) 3. Efraim Racker (1960) 4. Peter Mitchell (1961) 5. Masasuke Yoshida (1997) 6. Paul D. Boyer How is the pmf transmitted to the ATP synthesis? FoF1-ATPase

ATP Synthase Mitochondrial ATP synthase (complex V)  F-type ATP synthase  Similar to ATP synthase of chloroplast and bacteria  Two functional domains  F 1 : peripheral membrane protein  ATP synthesis  Isolated F 1 : ATP hydrolysis (originally called F 1 ATPase)  F o (o : oligomycin-sensitive)  Membrane integrated  Proton pore

ATP Synthase : F 1  3  3  (9 subunits)  Knoblike structure with alternating  and  arrangement   subunits; catalytic sites for ATP synthesis   subunit  Central shaft  Association with one of the three  subunits (  -empty)  Induction of conformational difference in  subunits  difference in ADP/ATP binding sites of  subunits    -ATP,  -ADP,  -empty

ATP Synthase : F o ab 2 c (3 subunits)  C subunit  Small (Mr 8,000), hydrophobic two transmembrane helices  Two concentric circles  Inner circle : N -terminal helices  Outer circle (55 Å in diameter) : C -terminal helices

Mechanism of ATP synthesis in F 1 18 O-exchange experiment with purified F 1  Incubation of purified F 1 with ATP in 18 O-labelled water  Analysis of 18 O incorporation into P i  3 or 4 isotopes in P i  Repetitive reaction of both ATP hydrolysis and ATP synthesis ; ADP + P i  ATP + H 2 O,  G ’o ≈ 0  reversible reaction!

Mechanism of ATP synthesis in F 1 Kinetic study for confirmation of  G ’o ≈ 0 Enz-ATP  Enz-(ADP + P i )  K’ eq = k -1 /k 1 = 24 s -1 /10 s -1 = 2.4   G ’o ≈ 0  differ from ATP (free in solution) hydrolysis  G ’o = kJ/mol (K’ eq =10 5 )  F o F 1 has high affinity to ATP (K d < M) than ADP (K d ≈ M)  40 kJ/mol difference in binding energy  Equilibrium toward ATP synthesis Release of ATP from the enzyme surface ; major energy barrier (not ATP formation)  Proton gradient makes it possible