Elucidating a Complex Mechanism.

ur understanding of the complex dynamic system dri v en by onformational change during adenosine triphosphate (ATP) ydr ol ysis by F 1 -ATPase is of fundamental biochemical imporance. 1 , 2 Cr yo-electr on micr oscopy (Cr yo-EM) studies 3 −5 have ontributed v alua b le structural information on how the F 1 TPase functions, although, in themselves, these have not led o a definiti v e mechanism. The F 1 -ATPase is a multi-subunit sysem containing 3 β-catalytic sites that have been studied by biohysical single-molecule experiments based on direct visualizaion of the rotation of its central γ -subunit. 6 However, it is difcult to esta b lish which interconverting site or sites contribute nergy for the observ ed r otation, gi v en that a site can perform he elementary chemical steps of ATP binding, ATP hydr ol ytic ond cleav a ge, and pr oduct (Pi and adenosine diphosphate, ADP) elease. 7 Originally, the molecular mechanism of ATP syntheis/hydr ol ysis w as studied using classical biochemical pproaches that provided a wealth of fundamental data. A i-site Boyer’s binding change mechanism of ATP syntheis/hydr ol ysis (Nobel Prize for Chemistry, 1997) was postulated etween 1973 and 1993 based on biochemical unisite/multisite atalysis and oxygen exchange experiments. 8 An alternati v e ri-site Nath’s torsional mechanism of energy transduction nd ATP synthesis/hydr ol ysis w as first pr oposed in 1999 and ev eloped ov er the next 25 yr using a nov el m ultidisciplinar y pproac h, 9 whic h inte gr ated physics, c hemistry, bioc hemistry, nd engineering. The dir ect measur ements by Senior and oworkers of the fluorescence quenching of tryptophan probes