Preparations of syringomycin purified from three isolates of Pseudomonas syringae pv . syringae according to published procedures have been shown to contain a group of structurally related peptides which can be resolved by HPLC on a reverse phase column . In the acid hydrolysate of all components serine, phenylalanine, 2,4-diaminobutyric acid and arginine in the ratio 2 :1 :2 :1 have been found . These products account for nearly 50% of the molecular weights determined by FAB mass spectrometry . Most of the antibiotic activity of the unfractionated preparations is recovered in a limited number of peaks .