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F1-ATPase is the catalytic, water-exposed sector of ATP synthase. In the isolated sector, ATP hydrolysis can drive rotation of a central shaft within a ring containing alternating alpha and beta subunits. In the complete membrane-coupled enzyme, rotation driven by the proton-motive force can instead support ATP synthesis. The direction depends on the coupled chemical and mechanical driving forces. ^[ref]

A direct experiment attached a fluorescent actin filament to the central gamma subunit and immobilized the surrounding assembly. On adding ATP, the filament rotated, making nanometre-scale motor action visible through a much larger pointer. This demonstrated rotation during hydrolysis; demonstrating membrane-driven synthesis requires the additional membrane sector and an appropriate driving gradient. ^[ref]

A researcher who coauthored high-speed measurements resolving rotational substeps of F1-ATPase. The experiment connected molecular motion with steps in an enzyme’s catalytic cycle rather than treating rotation as a smooth average.^[ref]