This study analyzed the free and
protein-bound forms of
dopa,
5-S-cysteinyldopa (5-S-CD), and
5-S-glutathionedopa (5-S-GD) in B16 and Harding-Passey (HP) mouse
melanomas to investigate the role of these
catechols for melanogenesis and melanosome morphogenesis, inasmuch as these
tumors produce melanosomes different in color and ultrastructure, i.e., eumelanosome type in B16 and pheomelanosome type in HP. Between B16 and HP mouse
melanomas, however, we found (a) no significant difference in the level of free
dopa and 5-S-CD in melanosomes and
tumors, although the levels of these
catechols reflected well the type of melanogenesis in control hair of normal mice, (b) a significant difference in free 5-S-GD level, which might, in part, reflect the observed difference in melanogenesis, and (c) no apparent difference in the level of bound
dopa and 5-S-CD in either melanosomes or
tumors. Thus, the striking difference in the color of melanosomes between B16 and HP
melanomas seems to be related primarily to the content--not the type--of
melanin pigments.