Detection of eumelanogenic and pheomelanogenic melanosomes in the same normal human melanocyte.

Ellipsoid and spheroid melanosomes similar to those found in the hair matrix melanocytes of eumelanic C57BL mice and pheomelanic Ay mice, respectively, have been shown to coexist in the same human melanocyte. The difference in the three-dimensional ultrastructure of these melanosomes of the human hair matrix melanocyte has been determined by high-voltage transmission electron microscopy using a goniometer. By energy-dispersive X-ray spectroscopy, sulfur, one of the main characteristic chemical properties of pheomelanin, is detected in a significant amount in each spheroid melanosome, but is absent in ellipsoid melanosomes. Furthermore, the internal structure of the spheroid melanosomes is dissolved by treatment with 0.5 N NaOH solution, whereas the ellipsoid melanosomes are not affected. We proposed that in normal human melanocytes pheo- and eumelanogenesis occurs in spheroid and ellipsoid melanosomes, respectively.