A NOVEL SUBUNIT OF VACUOLAR H-ATPASE RELATED TO THE B-SUBUNIT OF F-ATPASES()

The subunit structure of the vacuolar H+-ATPase (V-ATPase) membrane se ctor is not entirely known. The proteolipid is the only subunit that h as been implicated in the mechanism of energy transfer in the enzyme. We have identified a protein (M16) V-ATPase complex from Information o btained from the amino acid sequence of a proteolytic fragment of M16 was used to clone a bovine adrenal cDNA encoding this protein. The cDN A encodes a hydrophilic protein of 118 amino acid residues with a calc ulated molecular mass of 13 682 Da. Amino acid sequence analysis revea led that M16 exhibits a significant homology to subunit b of F-ATPases . M16 is smaller than subunit b and contains no apparent transmembrane segment in its N terminus. The remainder of subunit b is related to M 16 not only by its amino acid sequence but also in its predicted struc ture of helix-turn-helix. The structural and evolutionary implications of these findings are discussed.