F1-ATPase:: a highly coupled reversible rotary motor

F-1 (F-1-ATPase) is a highly coupled rotary molecular motor and hydrolyses three ATP molecules per turn (3 AT/turn). Recently, we have developed ferntolitre reaction chamber arrays for highly sensitive measurement of biological reactions. By combining this technique with the rotating magnetic tweezers, the coupling ratio of the reverse reaction, ATP synthesis catalysed by single F-1 molecules, has been investigated. The low coupling ratio of 10% (0.3 ATP/turn), catalysed by the alpha(3)beta(3)gamma subcomplex of F-1, was significantly improved to 77% (2.3 ATP/turn) after reconstitution of the epsilon subunit. This result revealed the novel function of the s subunit as a coupling factor of ATP synthesis catalysed by F-1. The possible mechanism for highly coupled ATP synthesis supported by the epsilon subunit is discussed.