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.