Transcript Biological Membranes and Energy Production

Biological Membranes and
Energy Production
Membranes as Energy Transducers
Inner leaflet
Outer leaflet
Asymmetry in chemical environments
Membrane Bilayer
Integral membrane proteins allow
formation of asymmetrical
environments
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]
Na+ channel
ΔGM= -nFE
ΔG= ΔGC + ΔGM
H+ gradients provide the energy necessary to
produce ATP
Chemical Energy
Light Energy
Electrical Energy
H+ gradient
ATP
H+ Gradients Perform a Number of Tasks
Oxidative Phosphorylation
Electron Transport Chain (ETC)
Sequence of e- transport
Redox Potential (V)
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complex II = no ATP
Inhibitors = discovery of complexes
Chemiosmotic Theory
I
II
4H+
III
IV
V
3H+
2H+
2H+
[H+]
[H+]
NADH NAD+ Succ Fum
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O2
H2O
ADP + Pi
ATP
The process of ATP production is catalyzed by a H+ Translocating ATPase
Termed chemiosmotic theory
Chemiosmotic theory requires four parameters
1)
2)
3)
4)
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
Complex V is a Multisubunit Protein
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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
–
–
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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
Protons Propel ATP Production
Conformational change
in β subunit
cap
stalk
Rotation of the γ subunit
Membrane
spanners
NOTE: this ATPase is reversible
3H+
Uncouplers of Oxidative Phosphorylation
1) Synthetic or Exogenous Uncouplers
1) Valinomycin
2) Ionophores
3) Protonophores (2,4-DNP)
2) Natural Uncouplers
the protein Thermogenin (UCP) found in brown adipose tissue