Vacuolar-type H(+)-ATPase with the a3 isoform is the proton pump on premature melanosomes

Cell Tissue Res. 2008 Jun;332(3):447-60. doi: 10.1007/s00441-008-0597-5. Epub 2008 Apr 12.


The melanosome, an organelle specialized for melanin synthesis, is one of the lysosome-related organelles. Its lumen is reported to be acidified by vacuolar-type H(+)-ATPase (V-ATPase). Mammalian V-ATPase exhibits structural diversity in its subunit isoforms; with regard to membrane intrinsic subunit a, four isoforms (a1-a4) have been found to be localized to distinct subcellular compartments. In this study, we have shown that the a3 isoform is co-localized with a melanosome marker protein, Pmel17, in mouse melanocytes. Acidotropic probes (LysoSensor and DAMP) accumulate in non-pigmented Pmel17-positive melanosomes, and DAMP accumulation is sensitive to bafilomycin A1, a specific inhibitor of V-ATPase. However, none of the subunit a isoforms is associated with highly pigmented mature melanosomes, in which the acidotropic probes are also not accumulated. oc/oc mice, which have a null mutation at the a3 locus, show no obvious defects in melanogenesis. In the mutant melanocytes, the expression of the a2 isoform is modestly elevated, and a considerable fraction of this isoform is localized to premature melanosomes. These observations suggest that the V-ATPase keeps the lumen of premature melanosomes acidic, whereas melanosomal acidification is less significant in mature melanosomes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Gene Deletion
  • Hydrogen-Ion Concentration
  • Melanocytes / ultrastructure
  • Melanosomes / chemistry
  • Melanosomes / enzymology*
  • Melanosomes / ultrastructure
  • Membrane Glycoproteins / analysis
  • Mice
  • Mice, Inbred C57BL
  • Mice, Inbred ICR
  • Phenotype
  • Pigmentation
  • Protein Isoforms / analysis
  • Vacuolar Proton-Translocating ATPases / analysis*
  • Vacuolar Proton-Translocating ATPases / genetics
  • Vacuolar Proton-Translocating ATPases / physiology
  • gp100 Melanoma Antigen


  • Atp6ap1 protein, mouse
  • Membrane Glycoproteins
  • Pmel protein, mouse
  • Protein Isoforms
  • gp100 Melanoma Antigen
  • Vacuolar Proton-Translocating ATPases