Role of D-amino acid in adaptation of organisms to environmental change

在发现D-丝氨酸作为哺乳动物脑NMDA受体的激动剂后，D-氨基酸在真核生物中的作用受到越来越多的关注。据报道，淡水螯虾在海水驯化后，肌肉中总游离D-丙氨酸积累超过30倍。本论文对D-氨基酸与环境胁迫的关系进行了研究，并对真核生物中D-氨基酸代谢相关酶进行了研究。从斑节对虾肝胰腺中发现丙氨酸消旋酶。对虾酶在免疫化学上与细菌酶不同，在分子量和亚基结构上与真菌酶不同。包括氯离子在内的单价阴离子通过稳定和活化参与酶的调节。这与D-丙氨酸在海洋和广盐性动物中作为α-调节剂的假设是一致的。我们还发现家蚕的丝氨酸消旋酶在最适pH、底物特异性和色谱行为等方面与大鼠脑丝氨酸消旋酶具有相似的性质。在化蛹阶段，D-丝氨酸的含量随着酶活性的增加而增加。本文还对粟酒裂殖酵母的三种氨基酸消旋酶Alr 1 p、Alr 2 p和Srf 1 p进行了研究。Alr 1 p是细菌丙氨酸消旋酶的同系物。A1 r2 p是细菌精氨酸消旋酶的分裂酵母对应物，Srf 1 p类似于低催化效率的大鼠丝氨酸消旋酶。这些消旋酶可能参与D-氨基酸的解毒。在这项工作中，我们还进行了筛选新的酶参与D-氨基酸代谢的海洋和广盐性动物在澳大利亚和美国。

After the finding that D-serine serves as an agonist of NMDA receptor of a mammalian brain, role of D-amino acids in eucaryotes has been received an increased attention. The fresh water crayfish has been reported to accumulate total free D-alanine by more than 30-fold in muscle after seawater acclimation. We are interested in the realtionship between D-amino acids and the environmental stress, and studied the enzymes related to the D-amino acid metabolism in eucaryotes. We found the alanine racemase from the hepatopancreas of the black tiger prawn, Penaeus monodon. The prawn enzyme is distinguishable immunochemically from bacterial enzymes and differs from fungal enzymes in the moleular weight and subunit structure. Monovalent anions including chloride are involved in the regulation of the enzyme through stabilization and activation. This is consistent with the hypothesis that D-alanine serves as an osmoregulator in marine and euryhaline animals. We also found that the silkworm has serine racemase which has similar properties to the rat brain serine racemase in pH optimum, substrate specificity, and behaviors upon chromatographies. At the stage of pupation, the contents of D-serine increased concomitantly with the increase in this enzymatic activity. In this work, we also studied the three amino acid racemases of Schizosaccharomyces pombe, Alr1p, Alr2p, and Srf1p. Alr1p is a homologs of bacterial alanine racemase. A1r2p is a fission yeast counterpart to bacterial arginine racemase, and Srf1p resembles a rat serine racemase in low catalytic efficiency. These racemases are probably involved in the detoxification of D-amino acids. In this work, we also performed the screening of new enzymes involved in the D-amino acid metabolism in marine and euryhaline animals in Australia and the United States.