Abstract
F1-ATPase is the smallest mechanical motor enzyme, which works for ATP synthesis. In addition, this enzyme shows ATP hydrolysis activity when the electrochemical proton gradient is insufficient or not utilized. To maintain the efficient ATP synthesis activity, this motor protein seems to be highly regulated in vivo. The γ subunit of cyanobacterial ATP synthase contains the inserted sequence at the middle region of the molecule in contrast to the other bacterial and mitochondrial ATP synthase γ subunits. Though the deletion of this region emerged the higher ATP hydrolysis activity (Konno, et al. 2006), the reason of the observed change of the activity has not been clarified up to now. Based on the rotation analysis, we successfully clarified that the increase of the ATP hydrolysis activity by deletion of this inserted sequence was simply due to a low sensitivity to the intrinsic inhibition mechanism, ADP inhibition. In addition, we found that the unique property of this enzyme to prone to ADP inhibition, which is easily induced by the inserted sequence of γ, has the physiological significance to maintain the cellular ATP level.
