detection of cross-linmd perides by fast atom b01wbardment mass spectrometry

the possibility of chemical modification of peptides and proteins under the condition of proteolytic digestions and fabms analysis was investigated. the results ;indicate that among the amino acid constituents of peptides and proteins: serinefcysteine, and cystine are the most sensitive residues which undergo chemical modificadons under the exprimenta1 conditions. the chemical modification of these amino acids which is governed by the intrinsic properties of the peptides will result in the formation of a molecular ion mass which is 16 mu lower than the molecufitir ion of the parent peptide, mhf. exact mass measurements of (mh-16) molecular ions indicate that these ions may cornspond to(mh-h o +h ) but not(mh-ch ) molecules. in addition, the results indicate the presence of no inter-and /or intrachain disulfide bond rearrangements uhder the experimental conditions of degradations and fabms analyses of lysozyme and rihonuclease a.