title: Photodissociation spectroscopy of protonated leucine enkephalin.
abstract: Protonated leucine enkephalin (YGGFL) was studied by ultraviolet photodissociation (UVPD) from 225 to 300 nm utilizing an optical parametric oscillator tunable wavelength laser system (OPO). Fragments were identified by absolute mass measurement in a 9.4 T Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Bond cleavage was preferred in the vicinity of the two aromatic residues, resulting in high ion abundances for a4, a1, b3, y2and y1fragments. a, b and y ions dominated the mass spectrum, and full sequence coverage was achieved for those types. Photodissociation was most effective at the short wavelength end of the studied range, which is assigned to the onset of the Laπ-π* transition of the tyrosine chromophore, but worked well also at the Lbπ-π* chromophore absorption maxima in the 35 000-39 000 cm-1region. Several side-chain and internal fragments were observed. H atom loss is observed only above 41 000 cm-1, consistent with the requirement of a curve crossing to a repulsive1πσ* state. It is suggested that the photochemically generated mobile H atom plays a role in further backbone cleavages, similar to the mechanism for electron capture dissociation. The b4fragment is most intense at the Lbchromophore absorptions, undergoing additional fragmentation at higher photon energies. The high resolution of the FT-ICR MS revealed that out of all x and z-type fragments only x3and x4were formed, with low intensity. Other previously reported x- and z-fragments were re-assigned to internal fragments, based on exact mass measurement.
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Leopold-Franzens-Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria. martin.beyer@uibk.ac.at.
authors.forename: Andreas
authors.initials: A
authors.lastname: Herburger
authors.forename: Christian
authors.initials: C
authors.lastname: van der Linde
authors.forename: Martin K
authors.initials: MK
authors.lastname: Beyer
mesh_terms: D004743:Enkephalin, Leucine / Q000737:chemistry*; D011522:Protons; D017550:Spectroscopy, Fourier Transform Infrared; D014466:Ultraviolet Rays
chemical_list: D011522:Protons; D004743:Enkephalin, Leucine