|Yoshikawa N, Okada S, Abe H.
|Molecular Characterization of Alanine Racemase in the Kuruma Prawn Marsupenaeus japonicus
|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.