Top-Down Mass Analysis of Protein Tyrosine Nitration: Comparison of Electron Capture Dissociation with “Slow-Heating” Tandem Mass Spectrometry Methods

Figure 1. ECD (a, b), IRMPD (c), and CID (d) MS/MS of mononitrated myoglobin. Nitrated tyrosine residues are circled in the fragment
summaries.

publication,⁴⁰ did not lead to the appearance of new ECD
fragments, although depletion of the charge-reduced ions was
observed, and the intensities of the ECD fragments increased in
comparison with the standard ECD. CID and IRMPD of nonre-
duced nitrated lysozyme produced only a few fragments, as they
could not cleave the disulfide bonds (data not shown). Lower
charge states, z < 10, of nonreduced lysozyme produced even
fewer MS/MS fragments than the 10+ state.

As expected, reduction/alkylation of the disulfide bonds
provided a remarkable improvement in the sequence coverage
by MS/MS. For bis-nitrated lysozyme, the total number of
fragment ions was 56, 47, and 21 from ECD, IRMPD, and CID,

Analytical Chemistry, Vol. 82, No. 17, September 1, 2010 7287

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