N-aspartate oxidase and free acidic D-amino acids in fish tissues

We describe the occurrence of D-aspartate oxidase activity and free D-aspartate and D-glutamate in several tissues of five fish species, carp (Cyprinus carpio), crucian carp (Carassius auratus langsdorfii), rainbow trout (Oncorhynchus mykiss), yellowtail (Seriola quinqueradiata) and sea bream (Pagrus major). N-methyl-D-aspartate was the best enzyme substrate, followed by D aspartate and D glutamate. The highest specific activity was observed in the liver, followed by the kidney and brain in the crucian carp and rainbow trout. In the other fishes, enzyme activities were similar in the liver and kidney and lower in the brain except the yellowtail. D-Aspartate (% of total) and D-glutamate (%) were detected with HPLC analysis in the tissues. With the exception of spleen of some species, D-glutamate concentration tended to be higher than those for D-aspartate, but D/(D+ L) ratios were higher for aspartate. (C) 1998 Elsevier Science Inc.