title: Support and challenges to the melanosomal casing model based on nanoscale distribution of metals within iris melanosomes detected by X-ray fluorescence analysis.
abstract: Melanin within melanosomes exists as eumelanin or pheomelanin. Distributions of these melanins have been studied extensively within tissues, but less often within individual melanosomes. Here, we apply X-ray fluorescence analysis with synchrotron radiation to survey the nanoscale distribution of metals within purified melanosomes of mice. The study allows a discovery-based characterization of melanosomal metals, and, because Cu is specifically associated with eumelanin, a hypothesis-based test of the 'casing model' predicting that melanosomes contain a pheomelanin core surrounded by a eumelanin shell. Analysis of Cu, Ca, and Zn shows variable concentrations and distributions, with Ca/Zn highly correlated, and at least three discrete patterns for the distribution of Cu vs. Ca/Zn in different melanosomes - including one with a Cu-rich shell surrounding a Ca/Zn-rich core. Thus, the results support predictions of the casing model, but also suggest that in at least some tissues and genetic contexts, other arrangements of melanin may co-exist.
authors.affiliation: Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany; Applied Physical Chemistry, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany; Analytical Chemistry - Biointerfaces, Ruhr-University Bochum, Bochum, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gorniak
authors.forename: Tamás
authors.initials: T
authors.lastname: Haraszti
authors.forename: Heikki
authors.initials: H
authors.lastname: Suhonen
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: Adam
authors.initials: A
authors.lastname: Hedberg-Buenz
authors.forename: Demelza
authors.initials: D
authors.lastname: Koehn
authors.forename: Ruth
authors.initials: R
authors.lastname: Heine
authors.forename: Michael
authors.initials: M
authors.lastname: Grunze
authors.forename: Axel
authors.initials: A
authors.lastname: Rosenhahn
authors.forename: Michael G
authors.initials: MG
authors.lastname: Anderson
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D007498:Iris / Q000378:metabolism*; D008543:Melanins / Q000737:chemistry; D020460:Melanosomes / Q000000981:diagnostic imaging / Q000378:metabolism*; D008670:Metals / Q000737:chemistry*; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008856:Microscopy, Fluorescence / Q000379:methods*; D011859:Radiography; D017356:Synchrotrons; D014965:X-Rays; D015032:Zinc / Q000737:chemistry
chemical_list: D008543:Melanins; D008670:Metals; C018362:pheomelanin; C041877:eumelanin; D003300:Copper; D015032:Zinc; D002118:Calcium
keywords: X-ray fluorescence analysis; eumelanin; melanosome; metal; pheomelanin; synchrotron-based imaging