The arginase pathway in Rhodobacter: Metabolism of L‐ornithine

The arginase pathway has been studied in three Rhodobacter strains. Arginase, urease, L‐ornithine 5‐aminotransferase and L‐ornithine cyclodeaminase activities have been detected in R. capsulatus and R. sphaeroides. These enzymatic activities were present in cells growing with nitrate of L‐glutamate and absent in the presence of ammonium as a nitrogen source. The basal levels of L‐ornithine 5‐aminotransferase and L‐ornithine cyclodeaminase measured in cells grown with L‐glutamate or nitrate were considerably enhanced in the presence of L‐ornithine. These results suggest that, in Rhodobacter strains, L‐arginine can be metabolized through the arginase pathway including two alternative pathways to glutamate semialdehyde with L‐ornithine at the branch point. Arginase, L‐ornithine cyclodeaminase and L‐ornithine 5‐aminotransferase were induced by L‐ornithine or L‐arginine and these enzymatic activities were also present in cells growing with L‐ornithine in the presence of ammonium.