title: Near edge X-ray absorption fine structure spectroscopy (NEXAFS) of pigment-protein complexes: peridinin-chlorophyll a protein (PCP) of Amphidinium carterae.
abstract: Peridinin-chlorophyll a protein (PCP) is a unique water soluble antenna complex that employs the carotenoid peridinin as the main light-harvesting pigment. In the present study the near edge X-ray absorption fine structure (NEXAFS) spectrum of PCP was recorded at the carbon K-edge. Additionally, the NEXAFS spectra of the constituent pigments, chlorophyll a and peridinin, were measured. The energies of the lowest unoccupied molecular levels of these pigments appearing in the carbon NEXAFS spectrum were resolved. Individual contributions of the pigments and the protein to the measured NEXAFS spectrum of PCP were determined using a "building block" approach combining NEXAFS spectra of the pigments and the amino acids constituting the PCP apoprotein. The results suggest that absorption changes of the pigments in the carbon near K-edge region can be resolved following excitation using a suitable visible pump laser pulse. Consequently, it may be possible to study excitation energy transfer processes involving "optically dark" states of carotenoids in pigment-protein complexes by soft X-ray probe optical pump double resonance spectroscopy (XODR).
authors.affiliation: Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2a, D-12489 Berlin, Germany.
authors.forename: Herbert
authors.initials: H
authors.lastname: Legall
authors.forename: Holger
authors.initials: H
authors.lastname: Stiel
authors.forename: Michael
authors.initials: M
authors.lastname: Beck
authors.forename: Dieter
authors.initials: D
authors.lastname: Leupold
authors.forename: Wieslaw I
authors.initials: WI
authors.lastname: Gruszecki
authors.forename: Heiko
authors.initials: H
authors.lastname: Lokstein
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D002338:Carotenoids / Q000737:chemistry*; D004141:Dinoflagellida / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D046912:Multiprotein Complexes / Q000737:chemistry; D015800:Protozoan Proteins / Q000737:chemistry*; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013057:Spectrum Analysis / Q000379:methods; D014965:X-Rays
chemical_list: D000596:Amino Acids; D045342:Light-Harvesting Protein Complexes; D046912:Multiprotein Complexes; D015800:Protozoan Proteins; C073227:peridinin chlorophyll-a protein, Dinophyceae; D002338:Carotenoids