SUMMARY: D-Arginine dehydrogenase activity was discovered in This enzyme was inducible by its substrate, D-arginine, as well as by its product, 2-ketoarginine, but not by L-arginine. The enzyme activity was measured , in the presence of artificial electron acceptors (phenazine methosulphate and iodonitrotetrazolium chloride). 2-Ketoarginine was catabolized further to 4-guanidinobutyraldehyde, 4-guanidinobutyrate and 4-aminobutyrate. Two enzymes involved, 4-guanidinobutyraldehyde dehydrogenase and guanidinobutyrase, were inducible by 2-ketoarginine; the latter enzyme was also strongly induced by 4-guanidinobutyrate. An arginine racemase activity was detected by an test. D-Arginine had the potential to be catabolized via the D-arginine dehydrogenase pathway and, after racemization, via the three L-arginine catabolic pathways previously demonstrated in In mutants blocked in the L-arginine succinyltransferase pathway, but not in the wild-type, L-arginine was channelled partially into the D-arginine dehydrogenase pathway. Mutations in the locus abolished growth of on 2-ketoarginine, agmatine and putrescine, and led to loss of 4-guanidinobutyraldehyde dehydrogenase and 4-aminobutyraldehyde dehydrogenase activities. Thus, these two activities appear to be due to one enzyme in The locus was mapped on the chromosome between and and was not linked to known genes involved in the three L-arginine catabolic pathways. The existence of four arginine catabolic pathways illustrates the metabolic versatility of


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