Analysis of Bacitracin B using fast atom bombardment and tandem mass spectrometry.

Bacitracin is a mixture of polypeptide antibiotics produced by the action of Bacillus subtilis and Bacillus licheniformis. The mixture has previously been shown to contain at least ten components, of which only the major component, Bacitracin A, and its oxidized counterpart, Bacitracin F, have been fully structurally evaluated. Using fast atom bombardment ionization with tandem mass spectrometry, three isobaric components of one of the minor constituents of the mixture, Bacitracin B, have been structurally characterized, delineating the three single substitution sites within Bacitracin A where Ile has been replaced by Val.