subunit, while in the P subunit the adenine is in contact with a hydrophobic interface

(20). Though the binding sites in the a subunits are highly specific, the roles remain

obscure.

The y subunit

 The y subunit plays an important role in the catalytic core. Interactions between the

amino- and carboxyl-terminal a-helices and the u3~ 3Subunits are responsible for the

conformational changes that result in ATP catalysis. The y subunit is a fundamental part

of the rotor stalk.

The Rotor Stalk

 Two narrow stalks, a centrally located stalk and a peripheral stalk, have been

observed to link the catalytic core of F1 and the membrane-bound proton translocating Fo

with about of 40-45 A+ in between (27). The central stalk came into view three decades

ago via EM and has since become widely referred to as the rotor stalk. The rotor stalk

consists of the y and a subunits. The bottom of the rotor stalk is connected firmly to the

Fo ring of c subunits located in the membrane and the top extends 90 A+ within the u3 3

hexamer of F1 where it forms crucial interactions with both the a and P subunits (57-59).

 F1Fo ATP synthase is an extraordinary enzyme due to its ability to couple potential

energy, obtained from proton translocation through Fo in the membrane, to the synthesis

of chemical energy, over 100 A+ away in Fl, by a rapid rotation of subunits. Although

predicted by Boyer in the 1970's, evidence of rotation did not appear until the early

1990's. The X-ray crystal structure solved by Walker's group suggested that the y

subunit was the rotating subunit by suggesting it could distribute itself to all three P

subunits as opposed to just one (20). Consistent with this idea was inhibition of the Fl