MASS-SPECTROMETRIC FRAGMENTATION OF THE PEPTIDE-CHAIN AND BETA-METHYL LANTHIONINE BRIDGES OF THE POLYCYCLIC PEPTIDE NISIN

The mass spectra of the antibiotic peptide nisin measured with plasma desorption mass spectrometry (PDMS) and liquid secondary ionization mass spectrometry (LSIMS) show similar fragmentation patterns. Neither PDMS nor LSIMS ionization result in reduction of the lanthionine or beta-methyl lanthionine bridges of intact nisin. It is proposed that many of the intense fragment peaks observed in the nisin mass spectra result from cleavage of both the peptide chain and the beta-methyl lanthionine bridges.