Fig. 8-4. F-ATP synthase
This consists of F1 and F0, with the F0 further divided into rotor and stator parts.
F-ATP synthase synthesizes ATP by coupling with the H+ transport that follows the concentration gradient of H+ (Fig. 8-4). This enzyme consists of F0 (the membrane intrinsic site) and F1 (the membrane superficial site). F0 consists of a rotor and a fixed part, between which channel-like paths for H+ transport are found. F1 involves ATP synthetic and degradative activities, and is also known as F-ATPase. If F1 is removed from the membrane, electron transport does not lead to ATP synthesis. For this reason, F1 was initially known as the coupling factor for electron transport and ATP synthesis. It was subsequently revealed that an enzyme of the same type as mitochondrial ATP synthase exists in chloroplasts and the cell membrane of eubacteria, and that it is widely involved in ATP synthesis; this enzyme is called the F-type (F stands for “factor”).
The important point in the coupling of H+ transport and ATP synthesis reactions is that, coupling with H+ transport, the rotor and the stalk rotate in a clockwise direction, thus supplying energy to F1. F1 does not rotate, and synthesizes ATP using the energy generated by the rotation of the stalk. The phenomenon of ATP synthase rotating like a motor as a reverse reaction has been demonstrated in an elegantly designed experiment (see the Column in 8.6). The details regarding the coupling of H+ transport and ATP synthesis are not covered here, but the stoichiometry is 3H+/ATP.