title: Dissociation kinetics of singly protonated leucine enkephalin investigated by time-resolved photodissociation tandem mass spectrometry.
abstract: The yields of post-source decay (PSD) and time-resolved photodissociation (PD) at 193 and 266 nm were measured for singly protonated leucine enkephalin ([YGGFL + H](+)), a benchmark in the study of peptide ion dissociation, by using tandem time-of-flight mass spectrometry. The peptide ion was generated by matrix-assisted laser desorption ionization (MALDI) using 2,5-dihydroxybenzoic acid as the matrix. The critical energy (E(0)) and entropy (DeltaS(++) at 1000 K) for the dissociation were determined by Rice-Ramsperger-Kassel-Marcus fit of the experimental data. MALDI was done for a mixture of YGGFL and Y(6) and the plume temperature determined by the kinetic analysis of [Y(6) + H](+) data were used to improve the precision of E(0) and DeltaS(++) for [YGGFL + H](+). E(0) and DeltaS(++) thus determined (E(0) = 0.67 +/- 0.08 eV, DeltaS(++) = -24.4 +/- 3.2 eu with 1 eu = 4.184 J K(-1)mol(-1)) were significantly different from those determined by blackbody infrared radiative dissociation (BIRD) (E(0) = 1.10 eV, DeltaS(++) = -14.9 eu), and by surface-induced dissociation (SID) (E(0) = 1.13 eV, DeltaS(double dagger) = -10.3 eu). Analysis of the present experimental data with the SID kinetics (and BIRD kinetics also) led to an unrealistic situation where not only PSD and PD but also MALDI-TOF signals could not be detected. As an explanation for the discrepancy, it was suggested that transition-state switching occurs from an energy bottleneck (SID/BIRD) to an entropy bottleneck (PSD/PD) as the internal energy increases.
authors.affiliation: Medical Proteomics Research Center, KRIBB, Daejeon, Korea.
authors.forename: Jeong Hee
authors.initials: JH
authors.lastname: Moon
authors.forename: So Hee
authors.initials: SH
authors.lastname: Yoon
authors.forename: Yong Jin
authors.initials: YJ
authors.lastname: Bae
authors.forename: Myung Soo
authors.initials: MS
authors.lastname: Kim
mesh_terms: D003373:Coumaric Acids / Q000737:chemistry; D004743:Enkephalin, Leucine / Q000737:chemistry*; D005841:Gentisates / Q000737:chemistry; D007700:Kinetics; D010455:Peptides / Q000737:chemistry*; D010777:Photochemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D003373:Coumaric Acids; D005841:Gentisates; D010455:Peptides; C007175:alpha-cyano-4-hydroxycinnamate; D004743:Enkephalin, Leucine; C010925:2,5-dihydroxybenzoic acid
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