Does a charge tag really provide a fixed charge

摘要: In biomolecule mass spectrometry, peptides are usually ionized by an acidic solvent or matrix. It is generally accepted that the mobilization of attached protons weakens backbone bonds and facilitates peptide fragmentation. While this often advantageous, it can lead to a multiplicity fragment ions (both N-terminal an, bn C-terminal yn ions). Formation too many types overly complicate spectra. Although very basic arginines tend sequester some extent simplify spectra, charge tags, small molecules containing permanent (for example, quaternary ammonium ion), have been proposed as even better solution problem. Charge-tagged localized positive assumed be absolutely fixed. Therefore, in MS/MS experiments, only Nterminal should formed through charge-remote mechanisms depending on position tag. Such simplified series contiguous would provide complete sequencing information ideal for spectral interpretation. Sensitivity also greatly improved after derivatization, since charge-tagged already need not protonated. However, lack mobile proton may reduce fragmentation efficiency which potential disadvantage. Most tags developed label N-terminus. Two popular examples trimethylammonium butyric acid (TMAB) tris(2,4,6-trimethoxyphenyl) phosphonium acetic (TMPP-Ac). Herein, we introduce (4-trimethylammoniumbutyryl (TMAB)) onto N-terminus several peptides. has reported modification improves detection sensitivity, leads production MALDI-PSD now demonstrate does always remain fixed at peptide. Figure 1a ESI spectrum Fibrinopeptide A. The presence single peak associated with doubly charged, derivatized (from tag one proton) indicates reaction between labeling reagent (TMAB-NHS; NHS= N-hydroxysuccinimide) was complete. Singly-charged A (ADSGEGDFLAEGGGVR) its derivative were isolated fragmented MALDI TOF/TOF apparatus. Results shown 1b 1c. As anticipated, dominant features because arginine residue. We had expected observe from TMABderivatized peptide, but surprisingly more complex (Figure 1c). case, Bn represents TMABlabeled b ion (Bn= bn+ 127). An* Bn* represent An lost trimethylamine (An*=An 59 Bn*=Bn 59). Hines et al. well Che Fricker. observed loss Remarkably, although supposed Nterminal, signals immonium ions, y 14 Da heavier than regular (y+ ions) still spectrum. These must protonated, despite there being no Observation y+ particularly remarkable. similar results GSFGSAIR FVDGSIR, indicating these chargetagged routinely undergo unexpected processes. 1. a) ESI-MS charged labeled (TMAB-ADSGEGDFLAEGGGVR), m/z 833.09 Da; MALDI-TOF/ TOF CID (1 kV) spectra singly b) c) TMAB derivative. See text details.