Vacuolar H+-ATPase domains are transported separately in axons and assemble in Torpedo nerve endings

Torpedo electric organ synaptosomes possess a typical vacuolar H+-ATPase (V-ATPase), inhibited by concanamycin A and insensitive to vanadate, made of the association of a catalytic soluble sector V1 to a membrane domain V0. In the electric nerves, the 57-kDa subunit B of the V1 sector was transported to the nerve endings by the slow axonal flow and did not accumulate upstream from an axonal block. In contrast, a 500% accumulation of the 15-kDa subunit c of the V0 membrane domain was observed, demonstrating that this subunit is conveyed by the fast axonal anterograde transport. After velocity sedimentation of solubilized nerve proteins, the 57- and 15-kDa subunits were recovered in different complexes corresponding, respectively, to the V1 and V0 domains. No fully assembled V-ATPase was detected. It is concluded that V1 and V0 domains of V-ATPase are transported separately in axons, at different rates, and that they only associate once arrived in nerve endings to form the active V-ATPase.