Direct measurement of the electrogenicity of the H+-ATPase from thermophilic bacterium PS3 reconstituted in planar phospholipid bilayers.

The proton-translocating ATPase of the thermophilic bacterium PS3 was incorporated into a planar phospholipid bilayer, and its electrogenicity was directly demonstrated. The enzyme (TF0F1) consists of a catalytic portion, F1, and a membrane-integrated portion, Fo. A short-circuit current of up to 1 nA/cm2 was generated upon the addition of ATP, and the direction of the current indicated the flow of positive charges from the TF1 side to the TF0 side. The generation of the electric current was progressively suppressed by the presence of an inhibitor of TF1 such as NaN3 or adenyl-5'-yl imidodiphosphate. An open-circuit membrane potential of 40-120 mV was also demonstrated (more negative on the TF1 side), which was inhibited by NaN3. Furthermore, an applied voltage of -180 mV (TF1 side negative) was sufficient to prevent the generation of electric current dependent on ATP hydrolysis, which indicated that the electrogenicity of TF0F1 is some 180 mV under the conditions studied. From these results it was tentatively concluded that the number of protons transported across the bilayer/mol of ATP is more than 3.