F1 ATPase from the thermophilic bacterium PS3 (TF1) shows ATP modulation of oxygen exchange

The ATPase from the ATP synthase of the thermophilic bacterium PS3 (TF1), unlike F1 ATPase from other sources, does not retain bound ATP, ADP, and Pi at a catalytic site under conditions for single-site catalysis [Yohda, M., & Yoshida, M. (1987) J. Biochem. 102, 875-883]. This raised a question as to whether catalysis by TF1 involved alternating participation of catalytic sites. The possibility remained, however, that there might be transient but catalytically significant retention of bound reactants at catalytic sites when the medium ATP concentration was relatively low. To test for this, the extent of water oxygen incorporation into Pi formed by ATP hydrolysis was measured at various ATP concentrations. During ATP hydrolysis at both 45 and 60 degrees C, the extent of water oxygen incorporation into the Pi formed increased markedly as the ATP concentration was lowered to the micromolar range, with greater modulation observed at 60 degrees C. Most of the product Pi formed arose by a single catalytic pathway, but measurable amounts of Pi were formed by a pathway with high oxygen exchange. This may result from the presence of some poorly active enzyme. The results are consistent with sequential participation of three catalytic sites on the TF1 as predicted by the binding change mechanism.