Proton translocating ATPase: its pump, gate, and channel

Abstract

Proton translocating ATPase of oxidative phosphorylation was divided into three functional units: pump, channel, and gate. This was achieved by the use of highly stable pure ATPase obtained from a thermophilic bacterium PS3. The pump and gate were found in a catalytic moiety of the ATPase called TF1, and the channel was in the remaining hydrophobic moiety of the ATPase called TF0 which rendered TF1 sensitive to energy transfer inhibitor such as DCCD. TF1 was composed of five subunits (alpha, 56,000; beta, 53,000; gamma, 32,000; delta, 15,500; epsilon, 11,000 daltons). The essential component of the pump was beta-subunit, since beta gamma-complex or alpha beta delta-complex showed ATPase activity. The gate which blocked passive leakage of protons through TF0 in the proteoliposomes was shown to be gamma delta epsilon-complex in TF1. Both delta- and epsilon-subunits were required to connect alpha beta gamma-complex to TF0. TF0 was identical to the channel and was composed of three kinds of subunits (19,000, 13,500, and 5,400 daltons) and the smallest one was [14C]-DCCD binding protein. When the ATPase was incorporated into vesicles containing highly stable saturated branched phospholipids, ATP-driven electrochemical potential of proton (delta mu H+ = 253mV) and proton gradient driven net synthesis of ATP were demonstrated. For these activities, pump, channel, and gate of proton translocating ATPase were all required.