Fundamentals of Biochemistry Third Edition Donald Voet • Judith G. Voet • Charlotte W. Pratt Chapter 18 Electron Transport and Oxidative Phosphorylation Copyright © 2008 by John Wiley & Sons, Inc.

We have made small amounts of ATP so far The main product is the 24 H+ (24 e-) that are produced

Mitochondrion

Cristae are not necessarily uniform structures Cristae are not necessarily uniform structures. They can vary greatly, restricting local ion movement, creating a large pH gradient.

How does NADH get into Matrix Aspartate-Malate shuttle Glycerophosphate shuttle Insect muscle Same power to weight ratio as a small car engine

Transport of Materials ATP/ADP Translocator One for one Charge problems Phosphate Symporter Phosphate and H+ Both driven by pH gradient

Efficiency of ETC Δε°’= -0.315 V Δε°’= 0.815 V If 1 NADH makes 2.5 ATP and it takes 30.5 kJ/mol to make 1 ATP Efficiency of ATP synthesis is ~100kJ/mole / 218kJ/mol = 35%

Inhibitors of ETC Complex I Complex IV Complex III

10 in humans

Complex I

Rhodopsin – Model Proton Pump

Complex II Complex I and Complex II are not sequential, but accept electrons from different sources. Complex I – NADH Complex II - succinate

Complex III Pass electrons from CoQ to cytochrome c Electrons in Complex III must go from a 2 e- carrier (CoQH2) to a 1 e- carrier, cytochrome c.

Q cycle Q-cycle involves two cycles Proton pumping of complex III is different from complex I or II

Complex IV Requires 4 electrons Contains Cu and Fe

Reaction center requires 4 electrons at once Fe(II)-Cu(I) contributes only 3 electrons Fourth electron comes from Y244 forming a tyrosyl radical

Chemiosmotic Theory 1961 Peter Mitchell Observations OP needs intact inner mitochondrial membrane Inner MM impermeable to H+, OH-, K+, Cl- ET sends H+ out Compounds that increase permeability of the MM inhibit ATP synthesis

Harnessing the Energy The free energy of sending a proton against the gradient is approximately 22 kJ/mol The free energy required to synthesize one ATP is approximately 40-50 kJ/mol It takes 2-3 H+ ions moving with the gradient to provide the energy to synthesize 1 ATP

ATPase portion Membrane portion

F1 region of ATP synthase Only beta subunits can catalyze ATP synthesis

ATP synthesis ADP + Pi bind to L site Free energy drives conformational change Only T site catalyzes ATP synthesis ATP is release following next conformational change

pH=8 pH=5 Only the c ring moves, not alpha and beta parts Arg210

PO Ratios ATP synthesized(P)/Oxygen reduce(O) 2 electrons through Complex I, III, IV result in 10 protons which rotates the c subunits one revolution thereby synthesizing 3 ATP 2 electrons from FADH2 enter complex II and result in 6 protons or ~2ATP Estimates for glucose 2.5 ATP/NADH; 10 NADH/glucose 1.5 ATP/FADH2; 2 FADH2/glucose 2 ATP/glucose from glycolysis 2 ATP/glucose from citric acid cycle Total = 32 ATP/glucose

Uncoupling Leads to Generation of Heat Diet pill?