MOLECULAR ANALYSES OF FREE D-AMINO ACID METABOLIZING ENZYMES IN AQUATIC ORGANISMS

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In order to understand the physiological functions of free D-alanine (Ala) found in large amount in aquatic crustaceans and some bivalve mollusks, we determined the primary structure of alanine race mase (ARase) catalyzed the interconversion between D-and L-Ala. ARase cDNA cloned, from the muscle and hepatopancreas of kuruma prawn Penaeus japon.icus for the first time in higher eukaryotes consisted of 1,798bp nucleotide sequence including the ORF encoding 421 amino acid residues.cDNA of D-amino acid oxidase (DAO) was cloned from the hepatopancreas of common carp Cyprlnus carpio for the first time in animals other than mammals. The cDNA contained 1,294bp including the ORF of 1,041bp encoding 347 amino acid residues.. The carp DAO was expressed in E. coil cells and purified to homogeneity. The recombinant DAO showed the highest activity against D-Ala. The enzymatical and structural characteristics of carp DAO positioned it between pig kidney and yeast DAOs.In carp fed the diet with D-Ala for 14days, DAO mRNA was strongly expressed in intestine followed by hepatopancreas and kidney, but not in muscle. The inducible nature of carp DAO indicates that it plays an important physiological role in metabolizing exogenous D-Ala that is abundant in their prey invertebrates, crustaceans and mollusks.