Isolation and characterisation of two degradation products derived from the peptide antibiotic nisin

Two degradation products of nisin have been isolated and their structures have been determined by 1 H NMR. Nisin 1–32 [(des‐ΔAla33‐Lys34; Val32‐NH 2 )nisin] and (des‐ΔAla5)nisin 1–32 [(des‐ΔAla5, ΔAla33‐Lys34; Ile4‐NH 2 , pyruvyl‐Leu6, Val32‐NH 2 )nisin] are formed on storage or by acid treatment. Contrary to previous reports, nisin 1–32 showed potent antimicrobial activity against Gram‐positive organisms comparable to that of nisin itself. (des‐ΔAla5)Nisin 1–32 , however, was biologically inactive, thus demonstrating the importance of ΔAla5 and/or ring A for biological activity.