Physiolozical role and biosynthesis of D-aminoacids in eukanyote

d -氨基酸作为真细菌细胞壁肽聚糖的组成部分是必不可少的。虽然一些d-氨基酸被发现是阿片样肽和抗生素（如环孢素A）的成分，但d-氨基酸在真核生物中的生理功能却很少受到关注。然而，最近分析技术的进步已经证明了d -氨基酸在包括哺乳动物在内的各种动物中的存在。在这项工作中，我们研究了真核生物中参与d -氨基酸生物合成的酶。我们发现在昆虫中存在吡哆醛磷酸依赖丝氨酸消旋酶。从家蚕（Bombyx mori）的蛹中部分纯化了该酶，并对其性质进行了研究。这是首次在真核生物中发现产生d -丝氨酸的丝氨酸消旋酶。对黑虎对虾（Penaeus monodon）肝胰脏丙氨酸消旋酶进行了部分纯化和鉴定。用免疫化学方法将该酶与细菌中的丙氨酸消旋酶区分开来。我们发现单价阴离子参与了黑虎酶的调控。这与d -丙氨酸参与几种海洋和泛盐无脊椎动物渗透胁迫反应的推测是一致的[9-14]。研究了嗜热脂肪嗜热芽孢杆菌丙氨酸消旋酶的反应机理。

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.