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D-Glutamate, a novel d -amino acid found in animal tissues, exclusively exists in the male reproductive tissues of the kuruma prawn, Marsupenaeus japonicus. Herein, changes in the d -glutamate content were determined in the male reproductive tissues of M. japonicus during acclimation to breeding seawater temperatures of 18–22°C and unilateral eyestalk ablation. The d -glutamate content in the testis increased with increasing seawater temperature and with unilateral eyestalk ablation. This suggests that both stimulations induced d -glutamate synthesis in the testis. Although the d -alanine content in the testis increased after unilateral eyestalk ablation, it did not change with elevated seawater temperature. Furthermore, we determined the d -glutamate distribution in the M. japonicus spermatophore. This indicates that d -glutamate is crucial in prawn fertilization. [ABSTRACT FROM AUTHOR]

Some aquatic invertebrates contain free d -alanine. We previously showed copious amounts of free d -glutamate, a novel d -amino acid, in the tissue of the male reproductive organs of Marsupenaeus japonicus. Herein, we clarified the distribution and potential role of d -glutamate and d -alanine in male reproductive tissues, namely the testis, vas deferens and seminal receptacle at different growth stages of M. japonicus. The percentage of d -glutamate to total glutamate was over 50% in these tissues. In particular, the content of d -glutamate was the most abundant in the vas deferens, the ratio of d -glutamate to total glutamate was approximately 80%. In contrast, d -alanine content was the lowest in the vas deferens among these tissues. d -Glutamate content was the highest when the prawn weighed 12 g, indicating that d -glutamate is actively synthesized in the younger stage. Our findings suggest that d -glutamate plays an important role in the reproductive functions of M. japonicus. [ABSTRACT FROM AUTHOR]

Aquatic crustaceans and some bivalve mollusks are known to contain copious amounts of free d-alanine in their tissues. For the first time in the animal kingdom, we have isolated a cDNA clone encoding alanine racemase from the muscle and hepatopancreas of the kuruma prawn Marsupenaeus japonicus. The recombinant enzyme expressed in Escherichia coli exhibited alanine recemase activity. The deduced amino-acid sequence showed only 23–31% identity to bacterial alanine racemases. However, the active site residues and some residues that interact with pyridoxal 5′-phosphate were also conserved in M. japonicus enzyme. There was higher alanine racemase mRNA expression in hepatopancreas than in muscle. In contrast, the d-alanine content in hepatopancreas was lower than that in muscle, suggesting that the physiological functions of free d-alanine may differ among tissues. These data suggest that the alanine racemase gene has been conserved from bacteria to invertebrates throughout a long evolutionary time scale. [ABSTRACT FROM PUBLISHER]