Occurrence of free D-aspartic acid in marine macroalgae.

The biologically rare D-aspartic acid was found in extracts of marine macroalgae. DL-aspartic acid was isolated from the Phaeophyta, Hizikia fusiformis, by ion-exchange chromatography, and crystallized from aqueous ethanol. It was characterized by optical-rotatory-dispersion analysis and reversed-phase HPLC analysis. The crystal consisted of equal amounts of D and L isomers. The presence of free D-aspartic acid was verified in 15 species from among 20 species of marine macroalgae by the same method (HPLC). Generally, Phaeophyta contained a high concentration of D-aspartic acid in contrast with the low concentration in Phycophyta and Rhodophyta. Particularly in Costaria costata, Hizikia fusiformis and Sargassum yezoensis, belonging to Phaeophyta, D-aspartic acid was found in concentrations proportional to those of L-aspartic acid.