Activated ion electron capture dissociation for mass spectral sequencing of larger (42 kDa) proteins

In previous studies, electron capture dissociation (ECD) has been successfu l only with ionized smaller proteins, cleaving between 33 of the 153 amino acid pairs of a 17 kDa protein. This has been increased to 99 cleavages by colliding the ions with a background gas while subjecting them to electron capture. Presumably this ion activation breaks intramolecular noncovalent b onds of the ion's secondary and tertiary structure that otherwise prevent s eparation of the products from the nonergodic ECD cleavage of a backbone co valent bond. In comparison to collisionally activated dissociation, this "a ctivated ion" (AI) ECD provides more extensive, and complementary, sequence information. AI ECD effected cleavage of 116, 60, and 47, respectively, ba ckbone bonds in 29, 30, and 42 kDa proteins to provide extensive contiguous sequence information on both termini; AI conditions are being sought to de nature the center portion of these large ions, This accurate "sequence tag" information could potentially identify individual proteins in mixtures at far lower sample levels than methods requiring prior proteolysis.