THE ARGINASE PATHWAY IN RHODOBACTER - METABOLISM OF L-ORNITHINE

The arginase pathway has been studied in three Rhodobacter strains. Ar ginase, urease, L-omithine 5-aminotransferase and L-ornithine cyclodea minase activities have been detected in R. capsulatus and R. sphaeroid es. These enzymatic activities were present in cells growing with nitr ate or L-glutamate and absent in the presence of ammonium as a nitroge n source. The basal levels of L-ornithine 5-aminotransferase and L-orn ithine cyclodeaminase measured in cells grown with L-glutamate or nitr ate were considerably enhanced in the presence of L-ornithine. These r esults suggest that, in Rhodobacter strains, L-arginine can be metabol ized through the arginase pathway including two alternative pathways t o glutamate semialdehyde with L-ornithine at the branch point. Arginas e, L-ornithine cyclodeaminase and L-ornithine 5-aminotransferase were induced by L-ornithine or L-arginine and these enzymatic activities we re also present in cells growing with L-ornithine in the presence of a mmonium.