Kinetic Analysis of Rotary F₀F₁-ATP Synthase

Abstract

F₀F₁-ATP synthase, which is found intrinsic to the membranes of bacteria, chloroplasts and mitochondria, uses proton-motive force to produce ATP from ADP and P_i (for a recent review see (1)). With respect to the chloroplastic ATP synthase the H⁺/ATP stoichiometry has been shown to be 4 (2–4). In a foregoing paper we presented the kinetic modeling of this enzyme, based on a comprehensive collection of experimental data (5). In the meantime, convincing evidence has been accumulated that during energy transduction the γ-subunit rotates relative to (αβ)₃ (6,7). The structural basis for a rotary mechanism of energy transduction has been outlined by Junge et al. (8,9). According to this picture the rotor is composed of the subunit complex γεc₁₂, while the stator is made up of the ensemble (αβ)₃δb₂a (see Fig. 1). Hypothetical models for torque generation by F₀ which resemble closely have been presented by several authors (9-11). According to the proposal of Boyer (12) rotation of γ relative to (αβ)₃ is assumed to induce the binding-change in F₁, which is coupled with the synthesis and release of ATP. In (5) we introduced γ as an elastic element which accumulates rotational energy generated by F₀ before it is transferred to F₁. Now, we will consider the detailed kinetic modeling of a definitive rotary mechanism of F₀F₁-ATP synthase.