Co-recipient of the Nobel Prize in Chemistry in 1997 along with Paul D. Boyer and Jens C. Skou for his elucidation of the mechanism for ATP synthesis in the F0F1-ATP synthase.

A member of the MRC Laboratory for Molecular Biology at Cambridge, John Walker has been recognized for his structural characterization of the ATP synthase through X-ray crystallography. Based on the structure, he was able to validate Paul D. Boyer's Binding Change Model for synthesis of ATP by the multi-subunit protein. He demonstrated that the protein behaved as an axle inside a cylinder with the gamma subunit rotating in a ring of alpha and beta subunits, changing their binding affinity for ATP and ADP. The energy driving this rotation is a proton gradient across the cell membrane.

A dramatic demonstration of this rotation was an experiment where an actin filament was covalently linked to the gamma subunit and the entire protein complex was then fixed to a glass slide. Adding ATP resulted in spinning of the gamma subunit with the actin filament swirling like a propellor as seen through a microscope!

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