[2P-44(YSA-1)] 1分子回転観察と操作によって解明されたミトコンドリア由来ATP合成酵素における阻害因子IF1の制御機構
F1-ATPase (F1) is the catalytic domain of ATP synthase (FoF1). Although the physiological role of FoF1 is ATP synthesis, F1 hydrolyzes ATP when proton motive force (pmf) collapses or F1 is isolated from Fo. To prevent wasteful consumption of ATP, mitochondrial F1 has an inhibitory subunit (IF1), which inhibits ATP hydrolysis by F1 under low pmf, but does not affect under normal pmf. Despite extensive structural analysis of the F1-IF1 complex, the regulation mechanism by IF1 remains unknown. Here, we have discussed IF1 inhibition based on the rotation mechanism revealed by single-molecule analysis. Rotations of F1 were visualized with magnetic beads. Once lapsed into IF1 inhibition, molecules never resumed rotation. To explore conditions where IF1 is released from F1, we have applied external force by magnetic tweezers to IF1-inhibited F1. As a result, rotations were resumed only when they were manipulated in the ATP-synthetic direction under a physiological condition including ADP and Pi. This finding agrees with the unidirectional regulation of IF1. We have also revealed that activation probability strongly correlated with rotary angle of F1, suggesting that IF1 release is tightly coupled with the elementary reactions executed by F1.