The arginase pathway inRhodobacter: 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.