Vacuolar-type H -ATPases (V-ATPases), which are composed of at least ten different subunits, can generate a proton-motive force by hydrolyzing ATP and acidify the contents of various intracellular organelles. Subunits A and B of V-ATPase have been detected immunologically in ascidian blood cells, predominantly in signet ring cells (vanadocytes), which accumulate vanadium in their vacuoles. The action of V-ATPase in ascidian blood cells has been demonstrated by the fact that bafilomycin A1, a specific inhibitor of V-ATPases, inhibits the acidification of the vacuoles of vanadocytes. As the next step in studying the function of V-ATPase in vanadocytes, we isolated cDNAs encoding subunits A and B of V-ATPase from the blood cells of an ascidian, Ascidia sydneiensis samea. The nucleotide sequences of the cDNAs for subunits A and B encoded proteins of 619 and 509 amino acids, respectively, both of which were highly conserved among organisms.
