Collisionally peptides

Both collisional activation (in ion traps) and post source decay (in curved field reflectron TOF analyzers) have been used successfully to obtain sequence ions from peptides prepared in situ on the sample holder. Single Dalton mass windows are advantageous for precursor selection, as are realized in ion-trap and trap-TOF configurations. Publicly available search algorithms can be used... 

Early studies have shown that tryptophan, tyrosine, histidine, methionine and cysteine, either as free amino acids or as components of peptides, are excellent substrates for O2 oxidation reactions. Usually, reaction of O2 with amino acids is mostly described in terms of chemical quenching with the exception of tryptophan, for which collisional deactivation as the result of physical quenching is not neghgible. The rate constants of O2 toward the main reactive amino acids that show a strong solvent dependence are reported in Table 2 for neutral aqueous solutions with values within the range 0.8-3.7... 

Figure 2. Collisionally induced dissociation (CID) spectra with doubly charged ions of a) m/z=649.4 and b) tn/z=S67.1. These spectra show that the ion at m/z=S67.1 is the b9 fragment of that at m/z 649.4. The CID specuum of the latter ion was consistent with the sequence of the known N-terminal peptide from cytochrome-C, namely Ac-Gly-Asp-Val-Glu-Lys -Gly-Lys -Lys -Ile-Phe, where the Lys residues have a deuterated acetylation. Ions labelled with an arrow pointing right are b fragment ions, those labelled with an arrow pointing left ate y fragment ions.

Figure 4. Collisional induced dissociation spectra of the peptide of mass 582 from the reversed phase chromatogram of peak 2 in figure 3. CID conditions are described in Methods.

The specific site of modification was established by high performance tandem MS experiments. In this technique the 12C isotope peak for the molecular ion in the first mass spectrometer is selectively introduced into an inert gas collision cell where fragmentation is induced. The fragments are separated and detected in the second mass spectrometer (22). Collisionally induced dissociation (CID) provides abundant structural information from which the amino acid sequence for the peptide (22) or, in this case, modified peptide can be deduced. 

Fig. 5. High energy collisionally induced dissociation mass spectrum for molecular ion MH+ m/z 1149 in fraction 9 (see Fig. la) corresponding to tryptic peptide P(133-144). Significant ions indicating the sequence are labeled.

Van der Kerk-Van Hoof, A. Heck, A.J.R. Covalent and Non-Covalent Dissociations of Gas-Phase Complexes of Avoparcin and Bacterial Receptor Mimicking Precursor Peptides Studied by Collisionally Activated Decomposition Mass Spectrometry, J. Mass Spectrom. 34, 813-819 (1999). 

These examples of this methodology show the usefulness of MS/MS, especially in the case of mixtures isomeric linkages can be identified peptide sequences (during either spontaneous or collisional-induced decompositions) can be determined. 

Measiuements of the emission anisotropy A as a function of added collisional quencher are made with the steady fluorescence intensity, which integrates the different weighted fluorescence lifetimes. Quenching emission anisotropy plot of 1 /A vs I (Fig. 5.14) yields for A(o) a value of 0.246 and 0.243 for [L-Met2] DREK and DREK, respectively. These values, lower than that (0.278) measured at - 45 °C for tyrosine at 280 nm (Lakowicz and Maliwal, 1983), indicate that tyrosine residue in both peptides display residual motion independent of the global rotation of the peptide. It is possible to measure the relative importance of the mean residual motions of the tyrosine residues ... 

Z (collisional frequency, fluorophore-quendter), 241 Zener dtode, 151 ZiiK-fingcr peptide, 88-89,416 Z-scale, 193... 

---