Occurrence of N-methyl-L-aspartate in bivalves and its distribution compared with that of N-methyl-D-aspartate and D,L-aspartate.

The presence of N-methyl-L-aspartate (NMLA) was demonstrated in bivalves, Corbicula sandai and Tapes japonica. To our knowledge, this is the first report on the occurrence of NMLA in animal tissues. NMLA in bivalve tissues was identified according to the following findings; (a) its derivatives with (+)- and (-)- 1-(9-fluorenyl)ethyl chloroformate (FLEC) behaved identically with those of authentic NMLA, respectively, on high-performance liquid chromatography (HPLC), (b) its derivatives with (+)- and (-)- FLEC behaved identically with (-)- and (+)-FLEC derivatives of authentic N-methyl-D-aspartate (NMDA), respectively, on HPLC and (c) its behavior on thin-layer chromatography was the same as those of authentic NMLA. We also describe the distribution of NMDA, and D- and L-aspartate, to which N-methylaspartate enantiomers are structurally related. NMDA was more widely dirtributed than NMLA in bivalves. These bivalves containing NMLA showed lower D-aspartate contents and D/(D+L) ratios of aspartate, than the bivalves containing NMDA.