Abstract
Free D-amino acids are widely distributed in living organisms, from bacteria to mammals, and play a key role in specific physiological functions. The origin of D-amino acids is not fully understood, but a specific racemase, which generates the D-form from its L-form, is responsible for this in at least some cases. In invertebrates, D-Ser, D-Asp, D-Ala and D-Arg have been found in various phyla species, and play important physiological roles. In contrast to the wide distribution of D-amino acids, amino acid racemase genes have been identified in few invertebrate species. We searched the nucleotide, EST, and SRA databases, and found 11 serine racemase homologous genes from eight invertebrate phyla species. The cloned genes were identified based on their maximum activity as serine racemase (SerR) and aspartate racemase (AspR). Our results revealed that SerR and AspR are more widely distributed among invertebrates than previously thought.
