The distribution of D-amino acids was examined on several tissues of kuruma prawn Marsupenaeus japonicus. D-Alanine was found in all tissues, and the ratio of D-alanine to total alanine ranged from 18.7 to 43.7% depending on the tissues. Of these tissues, muscle, heart, and gill contained a relatively large amount of D-alanine. Nervous tissue and eye, on the other hand, contained a large amount of D-aspartate. D-Glutamate was specifically detected in testis. The percentage of D-glutamate to total glutamate was over 50% in testis, suggesting the existence of the biosynthetic enzyme in this tissue. The changes of alanine racemase activity were determined in the muscle and hepatopancreas of M. japonicus before and after molting. The activity after molting increased twice in the muscle. On the other hand, it was not changed in the hepatopancreas. These data suggest that D-alanine plays an important role in the muscle during ecdysis. However, the free D-alanine level in the muscle was not changed significantly before and after ecdysis. From these data, several D-amino acids are considered to be utilized in some essential physiological phenomena in the different tissues of the prawn.
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