Produces ATP from ADP in the presence of a proton gradient across the membrane. The archaeal alpha chain is a catalytic subunit. ATP + 4 H(+)(in) + H2O = ADP + 5 H(+)(out) + phosphate Stimulated by sulfite, ethanol, glycerol, magnesium and zinc ions. Optimum pH is 5.2. Composed of seven subunits; A, B, C, D, E, F and G. Belongs to the ATPase alpha/beta chains family.