title: Structural characterization of allomelanin from black oat.
abstract: The brown to black coloration found in plants is due to the melanins, which have been relatively poorly investigated among the plant pigments. The aim of this work was to study the dark pigment extracted from the black oat hull with respect to composition and structure. Ultraviolet-visible (UV-Vis) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and Fourier transform infrared (FT-IR) spectroscopy were applied for the characterization of the pigment. UV-Vis spectroscopy revealed that the extracted material displays a broadband, structureless absorption profile a common feature of melanins. MALDI-TOF MS measurements demonstrated that oat melanin is a homopolymer built up from p-coumaric acid and consists mainly of low molecular weight (527-1499 Da) oligomers of 3-9 monomer units. The tetramer oligomer proved to be dominant. The results of the FT-IR analysis indicated that oat melanin is a fully conjugated aromatic system containing tetrasubstituted aromatic rings linked by CC coupling. The in vitro preparation of melanin from p-coumaric acid by horseradish peroxidase was performed for comparison. The resulting polymer consisted of oligomers of 4-9 monomer units similarly to those in oat melanin. However, the building blocks proved to be connected to each other via COC linkages in contrast with the CC linkages in oat melanin.
authors.affiliation: National Agricultural Research and Innovation Centre, Research Department of Field Crops, H-6726, Szeged, Alsókikötő sor 9, Hungary; Cereal Research Non-Profit Ltd., H-6726, Szeged, Alsókikötő sor 9, Hungary. Electronic address: varga.monika@noko.naik.hu.
authors.forename: Mónika
authors.initials: M
authors.lastname: Varga
authors.affiliation: Department of Physical Chemistry and Materials Science, University of Szeged, Aradi Vt. 1., H-6720, Szeged, Hungary.
authors.forename: Ottó
authors.initials: O
authors.lastname: Berkesi
authors.affiliation: Laboratory of Proteomics Research, Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, H-6726, Szeged, Temesvári krt 62, Hungary.
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Darula
authors.affiliation: Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, H-1117, Budapest, Hungary.
authors.forename: Nóra Veronika
authors.initials: NV
authors.lastname: May
authors.affiliation: Cereal Research Non-Profit Ltd., H-6726, Szeged, Alsókikötő sor 9, Hungary.
authors.forename: András
authors.initials: A
authors.lastname: Palágyi
mesh_terms: D018554:Avena / Q000737:chemistry*; D003373:Coumaric Acids / Q000737:chemistry; D008543:Melanins / Q000032:analysis*; D008970:Molecular Weight; D010858:Pigmentation; D011422:Propionates; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D003373:Coumaric Acids; D008543:Melanins; D011422:Propionates; C495469:p-coumaric acid
keywords: Avena sativa (Poaceae); FT-IR spectroscopy; MALDI-TOF MS; Melanin; Oat; p-Coumaric acid