I. R. Gibbons worked with K. E. Summers on the mechanics of flagella. Their 1971 experiment isolated sea-urchin sperm axonemes, briefly treated them with trypsin, and then added ATP. The partly digested structures actively separated as groups of outer microtubules slid relative to one another.[ref]
Adenosine triphosphate-induced sliding of tubules in trypsin-treated flagella of sea-urchin sperm by K. E. Summers and I. R. Gibbons. Abstract: isolated axonemes, limited proteolysis and ATP-induced sliding; PNAS 68, 3092–3096, 1971
The observation supported a mechanical explanation of bending: relative sliding can generate curvature when the intact structure resists unrestricted separation. Releasing some constraints made the underlying movement visible in a different form. This distinguishes a force-producing process from the larger structure that organizes that force into a useful motion.[ref]
Adenosine triphosphate-induced sliding of tubules in trypsin-treated flagella of sea-urchin sperm by K. E. Summers and I. R. Gibbons. Abstract: dark-field observations and proposed conversion of shearing forces to bending
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