SUBTILOPEPTIDASE A CLEAVAGE IN THE CYCLIC REGION OF THE PEPTIDE ANTIBIOTIC POLYMYXIN B1

Digestion of a commercial mixture of the peptides polymyxin B1 and B2 with subtilopeptidase A yielded a peptide whose amino acid composition corresponded to the ring fragment common to both antibiotics. However, in contrast to the earlier chemical studies of Suzuki and collaborators, our high resolution nmr studies indicated that the ring had been split. Edman degradation, hydrazinolysis and exopeptidase digestion showed the rupture to have occurred between positions 8 and 9.