Biological Membranes and Energy Production

1. Biological Membranes and Energy Production

2. Membranes as Energy Transducers Inner leaflet Outer leaflet Asymmetry in chemical environments Integral membrane proteins allow formation of asymmetrical environments Membrane Bilayer

3. Electrochemical Gradients can provide Energy The “downhill” motion of Na+ to the left provides a measureable electrical potential (E) across the membrane once Na+ ions reach equilibrium The magnitude of E can be calculated using Nernst equation E = RT/ZF ln [Na]L / [Na]R This downhill motion of ions can be translated into free energy change (ΔG). The movement of ions across a selectively permeable barrier is dependent on 1) voltage and 2) concentration gradient ΔGC= -RT ln [Nain]/ [Naout] ΔGM= -nFE Na+ channel ΔG= ΔGC + ΔGM

4. H+ gradients provide the energy necessary to produce ATP Chemical Energy Light Energy Electrical Energy H+ gradient ATP

5. H+ Gradients Perform a Number of Tasks

6. Oxidative Phosphorylation

7. Electron Transport Chain (ETC)

8. Sequence of e- transport • complex II = no ATP • Inhibitors = discovery of complexes Redox Potential (V)

9. Chemiosmotic Theory • The process of ATP production is catalyzed by a H+ Translocating ATPase • Termed chemiosmotic theory • Chemiosmotic theory requires four parameters • intact mitochondrial membrane • impermeable to ions that may dissipate the electrochemical gradient • ΔG of electron tranport is stored in a proton gradient which is used to produce ATP • The proton gradient can be sequestered, lowering ATP production. This event DOES NOT INHIBIT NADH OR SUCCINATE OXIDATION

10. Complex V is a Multisubunit Protein • FOF1 ATPase • Transmembrane protein (450KDa) • F0 subunit is the transmembrane H+ channel with 3 subunits (a=8, b=1, c=2) • H+ translocation depends on Glu • Determined by DCCD inhibition (prevents H+ translocation • Oligomycin blocks the F0 pump • F1 subunit is a soluble peripheral protein in the matrix • α3β3γδε subunits • β sudunit catalyzes ATP production

11. Protons Propel ATP Production Conformational change in β subunit cap stalk Rotation of the γ subunit Membrane spanners NOTE: this ATPase is reversible 3H+

12. Uncouplers of Oxidative Phosphorylation • Synthetic or Exogenous Uncouplers • Valinomycin • Ionophores • Protonophores (2,4-DNP)

13. 2) Natural Uncouplersthe protein Thermogenin (UCP) found in brown adipose tissue