Melanosomal pH controls rate of melanogenesis, eumelanin/phaeomelanin ratio and melanosome maturation in melanocytes and melanoma cells

Janis Ancans, Desmond J. Tobin, Martin J. Hoogduijn, Nico P. Smit, Kazumasa Wakamatsu, Anthony J. Thody*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

189 Citations (Scopus)


The skin pigment melanin is produced in melanocytes in highly specialized organelles known as melanosomes. Melanosomes are related to the organelles of the endosomal/lysosomal pathway and can have a low internal pH. In the present study we have shown that melanin synthesis in human pigment cell lysates is maximal at pH 6.8. We therefore investigated the role of intramelanosomal pH as a possible control mechanism for melanogenesis. To do this we examined the effect of neutralizing melanosomal pH on tyrosinase activity and melanogenesis in 11 human melanocyte cultures and in 3 melanoma lines. All melanocyte cultures (9 of 9) from Caucasian skin as well as two melanoma cell lines with comparable melanogenic activity showed rapid (within 24 h) increases in melanogenesis in response to neutralization of melanosomal pH. Chemical analysis of total melanin indicated a preferential increase in eumelanin production. Electron microscopy revealed an accumulation of melanin and increased maturation of melanosomes in response to pH neutralization. In summary, our findings show that: (i) near neutral melanosomal pH is optimal for human tyrosinase activity and melanogenesis; (ii) melanin production in Caucasian melanocytes is suppressed by low melanosomal pH; (iii) the ratio of eumelanin/phaeomelanin production and maturation rate of melanosomes can be regulated by melanosomal pH. We conclude that melanosomal pH is an essential factor which regulates multiple stages of melanin production. Furthermore, since we have recently identified that pink locus product (P protein) mediates neutralization of melanosomal pH, we propose that P protein is a key control point for skin pigmentation. We would further propose that the wide variations in both constitutive and facultative skin pigmentation seen in the human population could be associated with the high degree of P-locus polymorphism.

Original languageEnglish
Pages (from-to)26-35
Number of pages10
JournalExperimental Cell Research
Issue number1
Publication statusPublished - 1 Aug 2001

Bibliographical note

Funding Information:
We are pleased to acknowledge Drs J. Bonnet, J. Slats, and V. Bezrookove (Department of Molecular Cell Biology, LUMC) for their help with the microscopy and image analysis. This study was supported by Stiefel International.


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