COLLISON-ACTIVATED CLEAVAGE OF A PEPTIDE/ANTIOBIOTIC LINKAGE: EVIDENCE FOR GAS-PHASE INTRAMOLECULAR DISULFIDE EXCHANGE

Authors: Fagerquist, Clifton - Keith

Submitted to: American Society for Mass Spectrometry
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2003
Publication Date: 9/1/2003
Citation: FAGERQUIST, C.K. COLLISON-ACTIVATED CLEAVAGE OF A PEPTIDE/ANTIOBIOTIC LINKAGE: EVIDENCE FOR GAS-PHASE INTRAMOLECULAR DISULFIDE EXCHANGE. AMERICAN SOCIETY FOR MASS SPECTROMETRY. 2002.

Interpretive Summary:

Technical Abstract: Ceftiofur is a third generation beta-lactam antibiotic widely used in livestock for treatment of infections. Upon administration, ceftiofur is rapidly metabolized to desfuroylceftiofur, an antimicrobially active metabolite that has a free thiol functional group. Previous experiments using electron capture dissociation Fourier transform ion cyclotron resonance mass spectrometry (ECD-FT-ICR-MS) have confirmed that DFC binds to peptides and proteins through disulfide bonds [1,2]. In order to determine whether more commonly available dissociation techniques cleave the antibiotic/biomolecule binding, we have reacted DFC with two peptides (vasopressin and glutathione) and analyzed their reaction products by collision-activated dissociation tandem ion trap mass spectrometry (CAD/MS/MS). CAD/MS/MS of a vasopressin-DFC2 complex shows dissociative loss of one DFC (m/z 1513) and two DFC molecules (m/z 1084). CAD/MS/MS/MS of the fragment ion at m/z 1084 confirms the native cyclic structure of vasopressin is reformed and implies that a gas-phase intramolecular disulfide exchange has occurred which has never been previously reported in the scientific literature. CAD/MS/MS of glutathione-DFC shows dissociative loss of the peptide leaving the protonated [(DFC-2H) + H]+ (m/z 428) which may occur through a rearrangement of DFC prior complex fragmentation. The results suggest that CAD/MS/MS may be a useful technique for the detection of ceftiofur bound to peptide or proteins.