ε Subunit of Bacillus subtilis F1-ATPase Relieves MgADP Inhibition

MgADP inhibition, which is considered as a part of the regulatory system of ATP synthase, is a well-known process common to all F-1-ATPases, a soluble component of ATP synthase. The entrapment of inhibitory MgADP at catalytic sites terminates catalysis. Regulation by the epsilon subunit is a common mechanism among F-1-ATPases from bacteria and plants. The relationship between these two forms of regulatory mechanisms is obscure because it is difficult to distinguish which is active at a particular moment. Here, using F-1-ATPase from Bacillus subtilis (BF1), which is strongly affected by MgADP inhibition, we can distinguish MgADP inhibition from regulation by the epsilon subunit. The epsilon subunit did not inhibit but activated BF1. We conclude that the epsilon subunit relieves BF1 from MgADP inhibition.