Rudolph A. Marcus

What Can Be Learned about the Enzyme ATPase from Single Molecule Studies of its Subunit F1 and What Not?


Abstract

The transmembrane protein, F1Fo-ATP Synthase, is a rotary motor that synthesizes the widely used biochemical energy source, adenosine triphosphate (ATP), from adenosine diphosphate (ADP) and inorganic phosphate (Pi).1 The types of single molecule experiments on the F1 part include “stalling” and “controlled rotation” experiments using optical or magnetic methods, and unconstrained “free rotation” experiments. There are coordinated reactions in the three beta subunits of the F1, ADP plus Pi entrance, their reaction, and ATP release, typically studied in the reverse (hydrolysis) direction. The stalling and controlled rotation experiments are “quasi-static”, the rotation angle of the ATPase rotor being the slow variable, and with Dr. Sandor Volkan-Kacso we showed that using reaction rate theory devised for other problems one can make predictions of rate constant versus rotor angle in one type of such experiments from another, with no adjustable parameters, and treat composite events.2 Different features related to the opening and closing of the beta subunits of the F1 and the coupling of the chemistry to this mechanical motion were studied. The present state of understanding of these single molecule chemistry-mechanics experiments and what has been learned will be described.

1 E.g., review in W. Junge and N. Nelson, Annu. Rev. Biochem. 84, 231 (2015)

2 S. Volkán-Kacsó and R.A. Marcus, Proc. Natl. Acad. Sci. USA, 112, 14230 (2015); Proc. Natl. Acad. Sci. USA, 113,12029 (2016); Proc. Natl. Acad. Sci. USA, 114, submitted.


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