Kasho V N, Yoshida M, Boyer P D
Molecular Biology Institute, University of California, Los Angeles 90024-1570.
Biochemistry. 1989 Aug 22;28(17):6949-54. doi: 10.1021/bi00443a026.
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.
嗜热细菌PS3的ATP合酶中的ATP酶（TF1），与其他来源的F1 ATP酶不同，在单一位点催化条件下，催化位点不会保留结合的ATP、ADP和Pi [Yohda, M., & Yoshida, M. (1987) J. Biochem. 102, 875 - 883]。这就提出了一个问题，即TF1的催化是否涉及催化位点的交替参与。然而，当培养基中ATP浓度相对较低时，催化位点可能存在短暂但具有催化意义的结合反应物保留。为了对此进行测试，在不同ATP浓度下测量了ATP水解形成的Pi中水中氧的掺入程度。在45℃和60℃进行ATP水解时，随着ATP浓度降至微摩尔范围，水中氧掺入形成的Pi的程度显著增加，在60℃时观察到更大的调节。形成的大部分产物Pi是通过单一催化途径产生的，但通过具有高氧交换的途径形成了可测量量的Pi。这可能是由于存在一些活性较差的酶。结果与结合变化机制预测的TF1上三个催化位点的顺序参与一致。
