Catalytic subunit of the peripheral V1 complex of vacuolar ATPase. V-ATPase vacuolar ATPase is responsible for acidifying a variety of intracellular compartments in eukaryotic cells. ATP + 4 H(+)(in) + H2O = ADP + 5 H(+)(out) + phosphate V-ATPase is a heteromultimeric enzyme composed of a peripheral catalytic V1 complex (main components: subunits A, B, C, D, E, and F) attached to an integral membrane V0 proton pore complex (main component: the proteolipid protein). Two separate genes encode the catalytic 70 kDa V-ATPase subunit in psilotum and equisetum. Belongs to the ATPase alpha/beta chains family.