Summary ATP synthase

ATP is the main energy source for almost all
ATP synthase chemical processes in living systems
Protein synthesis
DNA replication




ATP
Muscle contraction
DNA injection



Soluble F1 ATPase Membrane bound F0




Why do we consume so much ATP? ATP, universal energy carrier of living systems
Many reactions in biological cells are thermodynamically
unfavorable (∆G > 0).
Hydrolysis
A thermodynamically unfavorable reaction can be driven
by a favorable one, if they are coupled.

A ↔ B ∆ G°' = +4 kcal/mol

K’ eq = [B]/[A] = 10 (- ∆ G°'/1.36) = 10 (- 4/1.36) =1.15 × 10 -3 Synthesis

No spontaneous formation of B, when [B]/[A] > 1.15 × 10 -3 , ATP + H 2O ADP + Pi
so most of A remains unconverted.
∆ G 0 = -12.2 kB T = -30.6 kJ/mol = -7.3 kcal/mol

We can make much more of B if we couple A ↔ B with a
∆G = ∆G 0 + ln ([ADP][P i ]/[ATP]) = -13.7 kcal/mol
favorable reaction.
~1/500




ATP hydrolysis shifts the equilibria ATP synthase is the ATP factory which
of coupled reactions synthesizes most of ATP in organisms
Coupled reaction:
A↔ B ∆ G°’ = + 4.0 kcal/mol Bacteria ATP synthase
ATP + H2O ↔ ADP + Pi + H + ∆ G°’ = - 7.3 kcal/mol
----------------------------------------- --------------------------- ATP synthase Mitochondria
A + ATP + H2O ↔ B+ ADP + P i + H + ∆ G°’ = -3.3 kcal/mol


[B]eq [ADP] eq [ Pi] e q
K'eq = ------------ • -------------------- = 10 ( - ∆ G° ' / 1.36) = 10 (- (-3.3) / 1.36 ) = 2.67 × 10 2
[A]eq [ATP] eq

[B]eq [ATP] eq
----- = K 'eq ---------------
[A] eq = [ADP] eq [Pi ] eq
Chloroplast
If the cell keeps it’s [ATP] / ([ADP] [Pi ]) ratio at about 500,
[B] eq/ [A] eq = 2.67 × 102 × 500 = 1.34 × 105, most of A has been converted!

Without ATP hydrolysis, this was 1.15 × 1 0-3, so A ↔ B conversion has
been increased by a factor of 108. ATP synthase




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, ATP synthase Structural Data ATP synthase is a rotary motor that couples
proton translocation to ATP synthesis
Cytoplasm
Yeast Stator

E. coli


~ 20 nm




H+ Rotor
Periplasm




ATP synthase is a rotary motor that couples One shaft, two motors
proton translocation to ATP synthesis ~100Å
ADP + Pi
F 1- ATPase
Soluble part, F1 -ATPase
Cytoplasm

-Synthesizes ATP when torque is
ATP applied to it (main function of this unit)
~80 Å - Produces torque when it hydrolyzes
ATP
- 5 subunits: 3α , 3 β , 1γ, 1δ and 1ε
~200 Å

~ 20 nm Membrane-bound part,
F0 Complex
~60 Å - Produces torque when positive
proton gradient across membrane
F o complex (main function of this unit)
- Pumps protons when torque is applied
~60 Å - 3 subunits: 1a, 2b and 9-12c).

Torque is transmitted between the motors via the central stalk.
Periplasm
H+
“ATP synthesis” requires both F0 and F1 parts.




Direct observation of ATP synthase rotary motion ATP synthesis mechanism
The applied torque causes rotation of the γ -subunit
which causes cyclic transformation of three catalytic sites.



αE
βE
βDP


α DP
α TP
βTP

Bottom view We have six nucleotide
binding sites, 3 catalytic
and 3 non-catalytic




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