High-sensitivity electron capture dissociation tandem FTICR mass spectrometry of microelectrosprayed peptides

Electron capture dissociation (ECD) has previously been shown by other rese arch groups to result in greater peptide sequence coverage than other ion d issociation techniques and to localize labile posttranslational modificatio ns. Here, ECD has been achieved for 10-13-mer peptides microelectrosprayed from 10 nM (10 fmol/muL) solutions and for tryptic peptides from a 50 nM un fractionated digest of a 28-kDa protein. Tandem Fourier transform ion cyclo tron resonance (FTICR) mass spectra contain fragment ions corresponding to cleavages at all possible peptide backbone amine bonds, except on the N-ter minal side of proline, for substance P and neurotensin. For luteinizing hor mone-releasing hormone, all but two expected backbone amine bond cleavages are observed. The tandem FTICR mass spectra of the tryptic peptides contain fragment ions corresponding to cleavages at 6 of 12 (1545.7-Da peptide) an d 8 of 21 (2944.5-Da peptide) expected backbone amine bonds. The present se nsitivity is 200-2000 times higher than previously reported. These results show promise for ECD as a tool to produce sequence tags for identification of peptides in complex mixtures available only in limited amounts, as in pr oteomics.