Nevertheless, the sequence of the fragment m/z 545.165 was
not successfully identified because the CID spectra only contained
a few fragments and a relatively high background interference.
This finding may be attributed to the poorer ionization of SeMetcontaining
peptides than their sulfur analogs (Ballihaut et al.,
2007). We also analyzed sub-fraction F3-3 (cf. Fig. 3b) by using
ESI FT-ICR MS and failed to detect any clear fragments that corresponded
to the Se isotopic pattern. The DEAE-Sepharose-FF
(Fig. 3b–d) and the HPLC-ICP-MS (Fig. 4) chromatograms also indicate
that the purity of the sample may present important implications
on MS analysis.