Biosynthesis of homoarginine and ornithine as precursors of the phytoeffector phaseolotoxin by the amidinotransfer from arginine to lysine catalyzed by an amidinotransferase in Pseudomonas syringae pv. phaseolicola

Abstract In the phytopathogenic Pseudomonas syringae pv. phaseolicola an amidinotransferase was detected and characterized which catalyzes the amidinotransfer from arginine to lysine producing the phaseolotoxin precursors homoarginine and ornithine. The enzyme was purified 419‐fold by affinity chromatography on homoarginine‐Sepharose. It had an apparent mol. wt. of 200 000 and exhibited MICHAELIS‐MENTEN kinetics with K m 7.7 mM for arginine and K m 4.2 mM for lysine. Ornithine competitively inhibited the enzyme with a K i of 0.8 mM. During cultivation of the pseudomonad the highest enzyme activity corresponds with the highest production rate of phaseolotoxin. At low toxin production, mutants exhibit a low enzyme activity and vice versa. Only those strains of different pathovarieties which are able to produce phaseolotoxin contain the enzyme. At 30 °C cultivation temperature, the enzyme activity was 50% of that at 18 °C, and toxin production decreased with increasing temperature. When microbes were grown on ribose, their enzyme activity was 60% lower than grown on glucose or glycerol. Toxin production was decreased to about 10% when growing on ribose. Amidinotransferase is considered to be one of the key enzymes of phaseolotoxin biosynthesis.