ε Subunit of Bacillus subtilis F(1)-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 ε 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 (BF(1)), which is strongly affected by MgADP inhibition, we can distinguish MgADP inhibition from regulation by the ε subunit. The ε subunit did not inhibit but activated BF(1). We conclude that the ε subunit relieves BF(1) from MgADP inhibition.