ATP Synthesis

How does the cell regenerate cytoplasmic NAD+?

Through aspartam-malate shuttles

Enzymes involved in the regeneration

• Transaminase

• Malate dehydrogenase

ATP synthase subunits

F₀ and F₁

F₀ subunit

1. Embedded in the IMM

2. Contains a c ring which rotates

3. Contains 2 proton half-channels

F1 subunit

1. In the mt matrix

2. Exists in 3 discrete conformations

Coupling of the F0 and F1 subunits

Rotation of the F0 gamma subunit physically pushes the F1 beta subunits through their 3-state cycle

Arg-210 residue

Sidechain residue in a ring: +ve and interacts w/ -ve charge in c-ring

How does the c ring rotate?

1. Proton enters half channel

2. -ve c-ring interacts w/ proton

3. Arg-210 is displaced (repulsion)

4. Arg-210 undergoes conformational change

5. Arg-210 interacts stronger w/ the c-ring -ve charge

6. Proton exits the 2nd half channel

Why is the F₀ c-ring subunit called a Brownian ratchet?

Bc the source of its rotation is thermal energy

Why must Brownian ratchets be rectified?

To avoid breaking the 2nd law of thermodynamics: it snaps into a new location and cannot rotate back

3 conformations of F1 subunits

1. Open: ADP+P_i/ATP in-and-out

2. Loose: ADP+P_i trapped

3. Tight: ADP+P_i converted

Proton/ATP ratio from ATP synthesis

12:3 or 4:1

Best comparison for ATP synthase

World’s smallest turbine generator

Max speed of ATP synthase

130 revolutions/sec

How is ATP exported out of the matrix?

Via ATP/ADP antiporter = 1 H+ used

Antiporter inhibitors

1. African herbal remedy

2. Tempeh bacteria

Efficiency of the ETC/ATP synthase mechanism

50% efficiency