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Differentiation between selected pairs of tripeptide diastereomers by tandem mass spectrometry on a hybrid tandem mass spectrometer

1993; Wiley; Volume: 7; Issue: 5 Linguagem: Inglês

10.1002/rcm.1290070507

1097-0231

Brenda L. Schwartz, Robert D. McClain, Bruce W. Erickson, Maurice M. Bursey,

Advanced Proteomics Techniques and Applications

Abstract Low‐energy collisionally activated decomposition (CAD) and unimolecular decomposition of the [M + H] + ions for X‐ L ‐Pro‐ L ‐Phe, where X is L ‐Ala, D ‐Ala, L ‐Asp, or D ‐Asp, allow easy differentiation between the LLL and DLL diastereomers. Tandem mass spectrometric (MS/MS) studies of the [M + H] + ions formed by fast‐atom bombardment (FAB) at various ion kinetic energies ( E lab values) on a hybrid tandem instrument produced ions of different intensities for the diastereomers. The ratio of NH 3 to H 2 O loss is 0.3 for the L ‐Ala peptide but 1.7 for the D ‐Ala isomer at 5 eV. In some L ‐Ala spectra, the [M + H − NH 3 ] + ion does not appear at all. The y 2 ion is up to twice as abundant in the L ‐Ala spectra as in the D ‐Ala, while the b 2 ion is somewhat more abundant for CAD of the D ‐Ala peptide for most collision energies investigated. The D ‐Asp peptide produces a b 2 ion that is more than half‐again as abundant as in the case of the L ‐Asp isomer, and an [M + H − H 2 O] + ion that is up to twice as abundant in the D ‐Asp CAD spectra as in those of the L ‐Asp. The y 1 , a 2 , and phenylalanine immonium ions are each up to twice as abundant in the L ‐Asp spectra as in those of the D ‐Asp isomer. The major differences are correlated with force‐field calculations on hydrogen‐bonded tautomers.