Proton Motive Force

Proton motive force

the energy-rich, unequal distribution of protons across the membrane

Chemical gradient

pH outside is 1.4 units lower than inside (more acidic)

Charge gradient

membrane potential (voltage difference) across the membrane is 0.14 V

ATP synthase units

F₀ unit and F₁ unit

F₀ unit

proton-conducting unit embedded in the inner mitochondrial membrane

composed of 8-14 c subunits + a + b₂ subunits

F₁ unit

catalytic unit with ATPase activity in the matrix

composed of 3 pairs of ⍺ / β subunits with active sites for ADP and Pi + 𝛾 + δ + 𝜀 subunits

a subunit

contains 2 half-channels that guide protons into and out of the c-ring

b subunit

forms part of the peripheral stalk that anchors F1 to the membrane portion

c ring (subunits)

ring of 8-14 identical subunits that rotate as protons pass through F₀

𝛾 subunit

rotates within the ⍺ / β hexamer to induce conformational changes during catalysis, the rotation of the c ring powers the movement of the 𝛾 subunit, which in turn alters the conformation of the β subunits

⍺ / β dimers

containing alternating open / loose / tight sites for nucleotide binding and ATP synthesis, rotation of the 𝛾 subunit interconverts the β subunits

𝛿 subunit

connects the peripheral stalk to the F1 head, maintaining structural integrity during rotation 

𝜀 subunit

stabilizes the central stalk and helps transmit torque from F₀ to F₁

c rings synthesize ATP

the number of c rings determine the number of protons required to synthesize a molecule of ATP (3 H+)

Actual ATP production of NADH and FADH2

NADH = 2.5 ATP

FADH2 = 1.5 ATP 

Theoretical ATP production of NADH and FADH2

NADH = 3.3 ATP

FADH2 = 2 ATP

2 shuttles for NADH

1. glycerol 3-phosphate shuttle

2. malate-aspartate shuttle

ATP-ADP translocase 

enables ATP to transverse highly impermeable inner membrane - exchanges cytoplasmic ADP —> mitochondrial ATP - translocase is powered by the proton-motive force