ATP synthesis (ATP synthase)

step 1

one H+ from inner mito. membrane space (cytosol) enters cmplx thru F₀ a-su, hydrophilic (enter) half-channel

• protonates Asp-61 on one of the c-su’s of c-su ring

• protonated Asp-61 now neutral/no charge → can be exposed to hydrophobic interior of inner mito. membrane when c-su ring rotates

• c-su ring rotates to allow next c-su to be protonated (very first step)

step 2

all of c-su’s of c-su ring are protonated (uncharged)

• when these rotate back to F₀ a-su, Asp-61 is deprotonated

• deprotonation releases proton to mito. matrix thru F₀ a-su, hydrophilic (exit) half-channel

step 3

c-su ring connected to γ (gamma)-su core → rotates 120 degrees w/in a3b3 hexamer

• γ (gamma)-su has 3 diff. interactive surfaces/faces that convert the b-su’s into 3 conformation types:

  • L-conf: “loose” → b-su can bind ADP and Pi

  • T-conf: “tight” → b-su converts bound ADP + Pi to ATP

  • O-conf: “open” → B-su can release ATP

calculations

dependent on # of c-su’s in ring

one complete rotation (360 degrees) of γ (gamma)-su makes 3 ATP (a3b3 hexamer, 3 catalytic sites)

number of c-su’s = # of H+ needed → divide H+ needed/ATP produced

amt of ATP made by NADH and FADH2

2.5 ATP/NADH

1.5 ATP/FADH2