F₁-ATPase (rotary engine)

1BMF

Abrahams et al., 1994 (PDB 1BMF) — bovine mitochondrial F₁-ATPase.

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Reaction cycle

1120° · γ turns a third of a revolution — a β-site binds ADP + Pi (loose)
2240° · the next step squeezes the site shut (tight) and forms ATP
3360° · the third step opens the site and releases ATP — 3 ATP per turn

Moving parts

γ-subunit (central crankshaft)
α₃β₃ catalytic headanchored

How it works

F₁ is the catalytic engine of ATP synthase — and the rotary motor that was famously filmed turning under the microscope. Three catalytic β-subunits alternate with three α-subunits around a central γ-subunit "crankshaft" (gold). As γ rotates, its asymmetric shape forces each β through the binding-change cycle — open → loose → tight — so every 120° step makes one ATP. Run in reverse, ATP hydrolysis drives γ around as a motor. Soluble (no membrane), it's the upper half of the complete ATP synthase shown alone.