Methabolism and functional role of D-aspartic acid and related compounds in marine animals.

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D-amino acids, which were viewed as natural oddities, have recently been found in various animals, plants and bacteria. In marine invertebrates it has been noted that D-alanine occurs in octopus muscle and D-aspartic acid(D-asp)in the nervous tissue of the cephalopods, Loligo, Sepia and Octopus. D-am'lno acids have also been reported in crustaceans, polychastes and bivalves. . These reports are however fragmentary studies, and the metabolism and the functional role of these D-amino acids are not known. This study was aimed to obtain the basic information on the distribution, metabolism and physiological function of D-amino acids especially D-asp in marine animals.On the course of the survey for the presence of free D-asp, an unknown large peak was found on the HPLC chromatogram of Aplysia kurodai- extract. It was isolated by ion-exchange chromatography using Dowex I and 50, and preparative high voltage paper electrophoresis and obtained as crystal. It was shown by optical rotatory dispersion spectrum and optical-resolusion HPLC analysis that this compound was consisted of equimolar amounts of Dasp and glycine. This compound resisted to the Edman's cleavage. This peptide was inferred to be beta-D-aspartylglycine and confirmed by synthesis.Thirty two species of marine animals were surveyed for the presence of free D-asp in their tissues. D-asp was found in all marine animals investigated. In marine invertebrates, D-asp occurred at levels of 20-60% of total Asp(D+L-form). Trace amount of D-asp was also detected in vertebrate(fish). Contrary, beta-aspartylglycine was detected only in Aplysia kurodai and A. juliana. Concerning the metabolism of D-asp in bivalve Mytilus e u is, the enzyme alanine oxaloacetate transaminase could be shown to be present in the mid-gut gland but not D-asp racemase or D-aspartate oxidase. L-alanine is most effective amino group donner to oxaloacetate to synthesis of D-asp in the tissue of M. edulis.