ENERGY TRANSDUCTION IN THE F-1 MOTOR OF ATP SYNTHASE

ATP synthase is the universal enzyme that manufactures ATP from ADP an d phosphate by using the energy derived from a transmembrane protonmot ive gradient. It can also reverse itself and hydrolyse ATP to pump pro tons against an electrochemical gradient. ATP synthase carries out bot h its synthetic and hydrolytic cycles by a rotary methanism(1-4). This has been confirmed in the direction of hydrolysis(5,6) after isolatio n of the soluble F-1 portion of the protein and visualization of the a ctual rotation of the central 'shaft' of the enzyme with respect to th e rest of the molecule, making ATP synthase the world's smallest rotar y engine. Here we present a model for this engine that accounts for it s mechanochemical behaviour in both the hydrolysing and synthesizing d irections. We conclude that the pi motor achieves its high mechanical torque and almost 100% efficiency because it converts the free energy of ATP binding into elastic strain, which is then released by a coordi nated kinetic and tightly coupled conformational mechanism to create a rotary torque.