Summary
The ultrastructure of melanosomes in mammalian epidermis has been studied using the freeze-fracture technique. The internal structure of the melanosome, as seen in cross-fractured granules, consists of a very fine particulate matter. There is no evidence of an internal membranous structure in melanosomes, indicating that the internal matrix which is characteristic of ultrathin sectioned material most likely represents cross-linked protein fibers.
Fracture ‘en-face’ of the melanosome limiting membrane reveals a random distribution of intramembrane particles on both the P- and E-faces of the membrane. There is a significantly higher density of IMPs on the P-face. The IMPs of the melanosome membrane may be involved in (a) selective passage of ions through the membrane, (b) membrane transducing events, and/or (c) anchoring sites for cytoplasmic fibrils and microfilaments.
Zusammenfassung
Wir haben die Ultrastruktur der Melanosomen in der Epidermis von Säugetieren mittels der Gefrierbruchtechnik studiert. Die innere Struktur der Melanosomen besteht in diesen Präparaten aus feinem, granulärem Material. Wir haben keinen Beweis für eine innere Membranstruktur der Melanosomen gefunden. Dies bedeutet, daß die innere Matrize, die für elektronenmikroskopische Schnitte charakteristisch ist, aus kreuzweise angeordneten Proteinfibrillen besteht.
Die “en-face”-Fraktur der Melanosomenmembran zeigt eine gleichmäßige Verteilung von intramembranösen Partikeln an der P- und E-Seite der Membran mit signifikant höherer Verteilungdichte an der P-Seite. Es wird angenommen, daß diese intramembranösen Partikel der Melanosomen (a) an dem selektiven Ionentransport durch die Membran und (b) an intramembranösen Übermittlerreaktionen beteiligt sind, bzw. (c) zur Verankerung von cytoplasmatischen Fibrillen und Mikrofilamenten dienen.
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Research supported by USPHS Grant AM-20669 from the National Institute of Arthritis, Metabolism, and Digestive Diseases
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García, R.I., Szabó, G. Freeze-fracture study of melanosomes in mammalian epidermis and the distribution of intramembrane particles in the melanosome membrane. Arch Dermatol Res 270, 1–6 (1981). https://doi.org/10.1007/BF00417143
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DOI: https://doi.org/10.1007/BF00417143