Characterization of biochemical properties of melanosomes for structural and functional differentiation: analysis of the compositions of lipids and proteins in melanosomes and their subfractions.
Two types of melanosomes were isolated from B16 and Harding Passey (HP) mouse melanomas to elucidate whether there are any features of melanosomal lipids and proteins related to the differences in morphology of melanosomes and in the biological activities of melanoma cells. Biochemical analyses were made to clarify (a) the lipid components of the 2 melanosomes and (b) the lipid and polypeptide compositions of their subfractions, i.e., the outer surface and inner core, resolved by a detergent, Brij-35, separately. We found (a) that the lipid contents in B16 melanosomes were much higher than those in HP, (b) that the B16 and HP melanosomes could be fractionated into a phospholipid-rich outer surface and phospholipid-poor core, (c) that both outer surface and core subfractions of HP were distinct from the corresponding subfractions of B16 with respect to phospholipid contents, (d) that the outer surface of B16 and HP revealed a polypeptide composition similar to each other, although the protein contents of the outer surface were much lower than those of core and (e) that the total melanosomes showed a marked difference in polypeptides between B16 and HP. In addition, both B16 and HP melanosomes revealed the alteration of lipid compositions, e.g., fatty acid acyl chain, similar to that observed during malignant transformation. There was not, however, any significant difference in acyl compositions between B16 and HP. It is likely that melanosomal lipid and protein not only affect the different morphogenesis of melanosomes but also reflect the different biological activities of whole cells, and that lipids, primarily located in the outer surface, regulate the functional aspects of melanosomes.