IDENTIFICATION AND CHARACTERIZATION OF A NOVEL 9.2-KDA MEMBRANE SECTOR-ASSOCIATED PROTEIN OF VACUOLAR PROTON-ATPASE FROM CHROMAFFIN GRANULES

Vacuolar proton-translocating ATPase (holoATPase and free membrane sec tor) was isolated from bovine chromaffin granules by blue native polya crylamide gel electrophoresis. A 5-fold excess of membrane sector over holoenzyme was determined in isolated chromaffin granule membranes. M 9.2, a novel extremely hydrophobic 9.2-kDa protein comprising 80 amino acids, was detected in the membrane sector. It shows sequence and str uctural similarity to Vma21p, a yeast protein required for assembly of vacuolar ATPase. A second membrane sector-associated protein (M8-9) w as identified and characterized by aminoterminal protein sequencing.