Physiolozical role and biosynthesis of D-aminoacids in eukanyote

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D-Amino acids are indispensable for eubacteria as components of the peptidoglycans of their cell walls. Although several D-amino acids were found as components of opioid-like peptides and antibiotics such as cyclosporin A, little attention has been paid to the physiological function of D-amino acid in eukaryotes.However, recent advances in analytical techniques have enabled the demonstration of D-amino acid in various animals including mammals. In this work, we have studied the enzymes which are involved in the D-amino acid biosynthesis in eukaryote. We found that pyridoxal phosphate-dependent serine racemase occurs in the insect. The enzyme was partially purified from pupae of silkworm, Bombyx mori, and its properties were studied. This is the first report of the occurrence of serine racemase in eukaryotes producing D-serine. We partially purified and characterizde the alanine racemase from the hepatopancreas of the black tiger prawn, Penaeus monodon. The enzyme was immunochemically distinguished from alanine racemase from bacteria. We found that monovalent anions are involved in the regulation of the black tiger enzyme. It is compatible with the speculation that D-alanine is involved in the osmotic stress response in several marine and euryhaline invertebrates[9-14]. We also studied the reaction mechanism of alanine racemase from thermophilic bacteria, Bacillus stearothermophilus.