Fragmentation Analysis of Bradykinin by 252Cf-Plasma Desorption Mass Spectrometry

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Abstract
The 252Cf-plasma desorption (PO) mass spectrum of the nonapeptide bradykinin was studied in detail with particular emphasis on the fragmentation pattern resulting from fast metastable decay of the molecular ion. N-acetyl and O-methyl derivatives of bradykinin were used as mass shift species for assignment of N-terminal and C-terminal fragment ions. Thirty-seven sequence-specific fragment ions were identified, including those that are due to cleavage of peptide backbone as well as side chain bonds (i.e., dn, vn, wn fragment ions). The degree of fragmentation correlates with what has been observed by fast atom bombardment tandem mass spectrometry using hi~h energy collisional activation. The high degree of excitation of bradykinin molecules in 252Cf-POMS is undoubtedly due to the special nature of excitation intrinsic to the 252Cf_PD process where electronic excitation occurs with a very high probability due to the high electron and photon flux surrounding the nuclear fission fragment track. These results offer further evidence that 252Cf_PDMS, in addition to providing molecular weight information, can be used to sequence peptides without the need for a second stage of molecular excitation.