title: Clarification of a peak at m/z 1634 from tryptically digested cytochrome c.
abstract: A peptide peak at m/z 1634 in the mass spectrum of tryptically digested cytochrome c has been ambiguously assigned to either a peptide IFVQKCAQCHTVEK or a peptide CAQCHTVEK combined with a heme group (CAQCHTVEK + heme (Fe(III))). A comprehensive investigation was performed to clearly identify the origin of the peak. Tryptic digests of cytochrome c were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), liquid chromatography-tandem MS (LC-MS/MS), LC-ultraviolet (LC-UV), and MALDI Fourier transform-ion cyclotron resonance (FT-ICR) MS. The use of instruments with extremely high mass accuracy revealed the mass difference between the IFVQKCAQCHTVEK and the (CAQCHTVEK + heme (Fe(III))) ions. Fragmentation of the peptide associated with the unknown peak yielded a heme ion and other fragment ions originating from a (CAQCHTVEK + heme (Fe(III))) ion. Furthermore, an absorption peak at 395 nm confirmed the presence of a heme group in the unknown peptide. High mass accuracy analyses of MS and MS/MS spectra, in addition to three-dimensional UV contour mapping, showed that the peak at m/z 1634 is due to a (CAQCHTVEK + heme (Fe(III))) ion and not from protonated IFVQKCAQCHTVEK.
authors.forename: Seongjae
authors.initials: S
authors.lastname: Shin
authors.forename: Hyo-Jik
authors.initials: HJ
authors.lastname: Yang
authors.forename: Jae-hyung
authors.initials: JH
authors.lastname: Kim
authors.forename: Jinhee
authors.initials: J
authors.lastname: Kim
authors.forename: Ji-hye
authors.initials: JH
authors.lastname: Lee
authors.forename: Kyu Hwan
authors.initials: KH
authors.lastname: Park
authors.forename: Hyun Sik
authors.initials: HS
authors.lastname: Kim
authors.forename: Jeongkwon
authors.initials: J
authors.lastname: Kim
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D014357:Trypsin / Q000378:metabolism
chemical_list: D007477:Ions; D010446:Peptide Fragments; D006418:Heme; D045304:Cytochromes c; D014357:Trypsin