ミトコンドリアにおけるATP合成のモデル反応

抄録

Mitochondrial F₁-F₀ complex catalyzes ATP synthesis coupled with proton translocation down the electrochemical potential gradient (Δμ_H⁺) across the inner membrane. F₁, the catalytic sector of the complex, can be detached from the membrane to be a soluble protein.
Recently, we found that soluble F₁ catalyzed ATP synthesis from medium ADP and Pi in the presence of dimethylsulfoxide (DMSO). This finding indicates that energy input of Δμ_H⁺ is not essential to covalent binding of ADP and Pi to form ATP on F₁. The synthesized ATP was bound to F₁ to compose F1-ATP complex, suggesting that the energy input is necessary for the release of ATP from F₁.
The F₁-ATP complex seemed to be formed also in the absence of DMSO. DMSO increased the affinity of F₁ for Pi and shifted the equilibrium between F₁-ATP complex and F₁-ADP-Pi complex.
Since it is the most simple ATP-synthesizing system ever known, it might be utilized to solve other problems about the mechanism of ATP synthesis. F₁ has two types of nucleotide-binding sites, tight binding sites and exchangeble binding sites. However, it has not been exclusively determined which is the catalytic site of ATP synthesis. We found that ATP was formed by soluble F₁ from ADP bound to the exchangeable binding site (s) but not from that bound to the tight binding sites.