Binding site states of the three β subunits in F1-ATP synthase During ATP synthesis, what is true about the nucleotide affinities of the three identical β subunits within the F1 sector?

Introduction / Context:
ATP synthase operates by a rotary catalytic mechanism. The three β subunits cycle through conformations that bind nucleotides with distinct affinities, enabling efficient ATP formation and release.

Given Data / Assumptions:

• F1 contains three αβ pairs; catalysis occurs on β subunits.
• The γ subunit rotation drives conformational changes.
• Classical states: O (open), L (loose), T (tight).

Concept / Approach:
In the binding-change mechanism, each β subunit alternates: O binds nucleotides weakly and releases ATP; L binds ADP + Pi loosely; T binds ATP tightly allowing synthesis. Thus, affinities for both ADP and ATP differ among subunits at any moment.

Step-by-Step Solution:
β(O): low affinity; product release.β(L): moderate affinity; ADP + Pi bound prior to catalysis.β(T): high affinity; ATP stabilized prior to release upon next rotation step.As γ rotates 120°, each β advances to the next state, changing its affinity profile for ADP and ATP.

Verification / Alternative check:
Single-molecule FRET and crystallographic snapshots show distinct nucleotide occupancies correlating with different affinities and conformations.

Why Other Options Are Wrong:
Limiting differences to ATP or to ADP alone is incorrect; both vary.Identical affinities (option d) contradict the binding-change mechanism.Option e is incorrect because nucleotide binding is central to catalysis.

Common Pitfalls:
Assuming all three catalytic sites behave identically at one time; forgetting the 120° stepwise rotation coupling.

Final Answer:
Different affinities for ATP and for ADP.