Fragmentation of tunichrome Sp-1 is dominated by an unusual gas-phase intramolecular rearrangement
✍ Scribed by Steven W. Taylor; Daniel B. Kassel; J. Andy Tincu; A. Grey Craig
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 152 KB
- Volume
- 38
- Category
- Article
- ISSN
- 1076-5174
- DOI
- 10.1002/jms.530
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✦ Synopsis
Abstract
Tunichrome Sp‐1 is a modified pentapeptide from the ascidian Styela plicata, having the structure H‐DOPA‐DOPA‐Gly‐Pro‐dcΔDOPA (where DOPA = 3,4‐dihydroxyphenylalanine and dcΔDOPA = decarboxy‐(E)‐α,β‐dehydro‐DOPA). The tandem mass spectrum of the peptide is dominated by a number of abundant fragment ions that involve a gas‐phase rearrangement where the dcΔDOPA group becomes covalently attached to the N‐terminus. The high degree of rearrangement in Sp‐1 compared with a related octapeptide, plicatamide, allowed for detailed multiple mass spectrometric (MS^n^) (up to n = 6) experiments, and hence permitted a detailed assessment of the origin and routes to the formation of the various rearrangement ions. Analyses on both a triple‐quadrupole and a quadrupole time‐of‐flight mass spectrometer were made to ascertain whether the gas‐phase rearrangements observed for tunichrome Sp‐1 were unique to an ion trap mass spectrometer (i.e. the hypothesis being that perhaps the extended trapping times were required to facilitate this unusual gas‐phase rearrangement). Interestingly, analyses on both the triple‐quadrupole and quadruple time‐of‐flight mass spectrometers revealed an identical phenomenon, with the rearrangement fragment ions present at approximately the same abundance as the non‐rearranged a‐, b‐ and y‐type sequence ions. We suggest that the smaller size of tunichrome Sp‐1 compared with plicatamide facilitates the transfer of the dcΔDOPA group in this gas‐phase rearrangement. This rearrangement was not observed for peptide analogs of tunichrome Sp‐1 that did not contain the dcΔDOPA at the C‐terminus, confirming that the presence of dcΔDOPA is critical for the rearrangement. Copyright © 2003 John Wiley & Sons, Ltd.