Title: The Site of Biosynthesis of Mammalian Tyrosinase11From the Research Laboratories of the Department of Dermatology of the Harvard Medical School at the Massachusetts General Hospital, Boston 14, Massachusetts and The Chester Beatty Research Institute, Institute of Cancer Research, Royal Cancer Hospital, London, S.W.3, England.This work was supported by Grant #CY-5010 of the National Institutes of Health, U.S. Public Health Service, Department of Health, Education and Welfare and by Grant 257-E …
Abstract: Melanosomes isolated from mouse melanoma by density-gradient centrifugation have been characterized as distinctive cell particles which are the site of melanin formation and are found within the cytoplasm of the melanocyte (1). The morphology of melanosomes and melanin granules has been revealed by electronmicroscopy. Birbeck and Barnicot (2) and Seiji, Fitzpatrick and Birbeck (1) have observed a series of steps in the formation of melanin granules within the melanocyte. Recently, Drochmans (3) has reported that in human and cat skin there appear, under the electron microscope, to be two distinct constituents in melanin granules: 1) a framework with what appears to be a crystallinelike structure, and 2) a diffuse component which seems to have no structure. This diffuse constituent has a relatively high density and seems to fill the space between the latticework of the structural component. Two kinds of melanin granules were distinguished in Drochman's study: light melanin granules which may correspond to melanosomes, and dense melanin granules. It has been suggested that there is a reciprocal relationship between degree of melani-zation and amount of measurable tyrosinase within the melanosome (4). Thus, the biological status of melanosomes and melanin granules in melanin-forming cells has been delineated both morphologically and biochemically.