BEAN HALO BLIGHT - COMPARISON OF PHASEOLOTOXIN AND N-PHOSPHOGLUTAMATE

Phaseolotoxin ([nδ-phosphosulphamyl]ornithylalanylhomoarginine) and phaseotoxin A (reported to be n-phosphoglutamic acid) are compounds that have been isolated by different workers from culture filtrates of the bean halo blight organism, Pseudomonas phaseolicola. This paper compares n-phosphoglutamate with phaseolotoxin in a number of tests. n-Phosphoglutamate was much less stable than phaseolotoxin in weakly acidic or alkaline aqueous solutions and, unlike phaseolotoxin, was susceptible to hydrolysis by phosphatase. n-Phosphoglutamate was not an effective inhibitor of ornithine carbamoyltransferase, whereas phaseolotoxin gave 50% inhibition when present in the assay mixture at a concentration of 0·3 μm. When 44 nmol n-phosphoglutamate was tested on bean leaves by the prick assay procedure, no chlorosis or ornithine accumulation resulted. In contrast 0·07 nmol phaseolotoxin gave chlorosis and ornithine accumulation, and 7 nmol led to the appearance of the systemic symptoms as well. It is concluded that n-phosphoglutamate lacks many of the properties to be expected in a bean halo blight toxin, and it is suggested that phaseotoxin A may instead be a compound related to phaseolotoxin. © 1979.