Biophysical studies on ATP synthase

The isolation of ATP synthase (F₀F₁) (82) and F₀ (83) 34 years ago finally revealed that F₀F₁ is a motor composed of F₀ (ion-motor, abc subunits) and F₁ (ATP-motor, α₃β₃γδε subunits) (Fig. 1). The single molecule videotape (4, 5, 65, 66) revealed that γε axis of F₁ rotates counterclockwise, proceeds by each $\text{2π}\text{3}$ step, and is driven by torque of 42 pN·nm (12) with nearly 100% efficiency (5) (Fig. 4). The motor is composed of a rotor (γε-F₀-c) and a stator (α₃β₃δ-F₀-ab), and the rotor is connected to a shaft (γε). Since F₀F₁ is driven by Δ$\text{}\text{̄}$gmH⁺ (9, 10, 84), biophysical studies on stable TF₀F₁ (1, 7) are essential to elucidate the mechanism. These include nanomechanics (4, 5) (Fig. 4), crystallography (2, 3) (Figs. 2 and 3), NMR (51, 52), ESR (56), synchrotron analysis (3, 28), and electrophysiology (10, 25). The K_mATP value of rotation is 0.8 μm, with the V_max of 3.9 rps (5). This corresponds to the bi-site catalysis in proton transport by F₀F₁ (10, 70, 84). X-ray crystallography of MF₁ (2) and the α₃β₃ oligomer of TF₁ (3) (Fig. 2) together with mutation analyses revealed the role of residues in the rotation. The idea of elastic energy store is proposed in α₃β₃γ during the stepping time (up to a few sec) after the ATP binding. Biological studies have partially clarified the genetic and kinetic regulation of the rotation in MF₁. Both theories (6, 7, 62, 64, 85) and the biological significance (17) of the intramolecular rotation of F₀F₁ await further studies, especially those of F₀ and minor subunits.