Chemical Properties of Syringomycin and Syringotoxin: Toxigenic Peptides Produced by Pseudomonas syringae

Syringomycin (SR) and syringotoxin (ST), wide spectrum antibiotics and phytotoxins isolated from ecotypic strains of Pseudomonas syringa , were purified to homogeneity and compared for their physicochemical properties. Acid hydrolysates of SR and ST were analysed for ninhydrin-reactive components by paper chromatography and the Durrum single-column method of amino acid analysis. Both active and base inactivated preparations of SR yielded substances tentatively identified as serine, phenylalanine, an unidentified basic amino acid, and arginine in a 2:1:2:1 mole ratio, respectively. Preparations of SR from ecotypic strains of P. syringae from pear, peach and millet hosts, had an identical amino acid composition which appeared to exclude a potential role of SR in the plant host specificity of P. syringae . ST isolated from a strain of P. syringae from a citrus host, contained substances tentatively identified as threonine, serine, glycine, ornithine, and the same unidentified basic amino acid found in SR in a 1:1:1:1:1 mole ratio. Although autoradiographs of paper chromatograms of acid hydrolysates of ¹⁴C-SR and various chromogenic reagents did not indicate the presence of substances other than amino acids, the nitrogen content of SR by combustion analyses was lower than expected which suggested the possible presence of another component.