title: A Soret marker band for four-coordinate ferric heme proteins from absorption spectra of isolated Fe(III)-Heme+ and Fe(III)-Heme+(His) ions in vacuo.
abstract: In this work, we report the absorption spectra in the Soret band region of isolated Fe(III)-heme+ and Fe(III)-heme+(His) ions in vacuo from action spectroscopy. Fe(III)-heme+ refers to iron(III) coordinated by the dianion of protoporphyrin IX. We find that the absorption of the five-coordinate complex is similar to that of pentacoordinate metmyoglobin variants with hydrophobic binding pockets except for an overall blueshift of about 16 nm. In the case of four-coordinate iron(III), the Soret band is similar to that of five-coordinate iron(III) but much narrower. These spectra serve as a benchmark for theoretical modeling and also serve to identify the coordination state of ferric heme proteins. To our knowledge this is the first unequivocal spectroscopic characterization of isolated 4c ferric heme in the gas phase.
authors.affiliation: Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark.
authors.forename: Morten Køcks
authors.initials: MK
authors.lastname: Lykkegaard
authors.forename: Anneli
authors.initials: A
authors.lastname: Ehlerding
authors.forename: Preben
authors.initials: P
authors.lastname: Hvelplund
authors.forename: Umesh
authors.initials: U
authors.lastname: Kadhane
authors.forename: Maj-Britt Suhr
authors.initials: MB
authors.lastname: Kirketerp
authors.forename: Steen Brøndsted
authors.initials: SB
authors.lastname: Nielsen
authors.forename: Subhasis
authors.initials: S
authors.lastname: Panja
authors.forename: Jean Ann
authors.initials: JA
authors.lastname: Wyer
authors.forename: Henning
authors.initials: H
authors.lastname: Zettergren
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006427:Hemin / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods; D055672:Static Electricity
chemical_list: D005290:Ferric Compounds; D006418:Heme; D006639:Histidine; D006427:Hemin