MELANOSOME AND LYSOSOME II. Digestion of Melanosome with Mouse Liver Lysosome

Swiss mice bearing melanomas received intraperitoneal injection of 14C-amino acid mixture and 14C-DOPA separately. Radioactive mitochondria and melanosomes were isolated from these mouse melanomas. In vitro degradation of 14C-amino acid labeled melanosomes and mitochondria was carried out with lysosomes isolated from mouse liver. The progressive degradation of protein moiety of mitochondria was observed and the slow but steady degradation of melanosomes was also brought about. In vitro degradation of 14C-DOPA labeled melanosomes was performed with liver lysosomes. There was no significant amount of degradation in vitro. From these experimental results, immature, less melanized melanosomes would be more susceptible than the mature, fully melanized melanosomes. It is assumed, therefore, that in the phagosomes, melanosomes can be degraded by lysosomes at the protein moiety and the mature melanosomes would be more resistant against lysosomal attack