Methabolism and functional role of D-amino acid in marine invertebrates.

D-氨基酸被认为是天然的奇怪物质，在各种动物、植物和细菌中都有发现。D-天冬氨酸(D-Asp)也在人类的蛋白质中被检测到，如眼睛晶状体、牙釉质和大脑。D-天冬氨酸被认为是疾病和衰老的原因和指标。因此，D-asp的发生在各种研究领域得到了越来越多的关注。在海洋无脊椎动物中，一些研究人员描述了个别D-氨基酸的孤立存在，或使用酶分析测量了D-氨基酸的未指明存在。为了解海洋无脊椎动物体内D-氨基酸的分布、代谢和生理功能的基本信息，采用光学分辨高效液相色谱法对除DL-赖氨酸外的14种组成蛋白质的DL-氨基酸中的13种进行了分析。然而，该方法能够在生物组织提取液中检测到天冬氨酸、谷氨酸、苏氨酸、精氨酸、丙氨酸、酪氨酸、Val、Ile和Leu等9种D-氨基酸。用该方法分析了几种海洋无脊椎动物的D-氨基酸。在所研究的几种海洋无脊椎动物中，只有两种D-氨基酸(D-天冬氨酸和D-丙氨酸)被证实。在布氏扇贝血液中检测到高浓度的D-天冬氨酸。D-和L-异构体的浓度比均小于1。D-天冬氨酸在所有其他物种中都检测到低浓度，尤其是在鳃中。文蛤体内D-丙氨酸含量显著升高。该种内收肌中D-丙氨酸的浓度是L-丙氨酸的3倍。D-ALA在亲缘关系良好的对虾和裸海胆中也有较高浓度的检测。将在50%海水中保存一周的慈菇转移到0、25、75和100%海水中，分析其DL-丙氨酸的浓度。在低盐度和高盐度条件下，D-ALA的变化幅度均大于L-ALA。

D-Amino acids, which were considered as natural oddities, have been found in various animals, plants and bacteria. D-Aspartic acid (D-Asp) has been also detected in human proteins like eye lens, tooth enamel and brain. D-Asp was proposed to be causes and indicators of diseases and aging. Occurrence of D-asp has therefore gained increasing attention in a variety of research fields. In marine invertebrates, several investigators have described either isolated occurrences of individual D-amino acids or have measured the unspecified presence of D-amino acid using enzyme assay. This study was aimed to obtain the basic information on the distribution, metabolism and physiological function of D-amino acids in marine invertebrates.Among fourteen DL-amino acids which compose protein, except DL-lysine, thirteen DL-amino acids were possibly analyzed by optical-resolution HPLC method. This method was however able to detect nine D-amino acids such as Asp, Glu, Thr, Arg, Ala, Tyr, Val, Ile and Leu, in biological tissue extracts. Several marine invertebrates were analyzed for D-amino acids using this method. Only two D-amino acids (D-asp and D-ala) were confirmed in several marine invertebrates examined. High concentration of D-Asp was detected in the blood shell Scapharca broughtonii. The concentration ratio of D- to L-isomer was below one. Low concentration of D-asp was detected in all other species especially in its gill. Significant concentration of D-Ala was detected in a clam Meretrix lusoria. The concentration of D-ala was three times higher than that of L-ala in the adductor muscle of this species. D-Ala was also detected in high concentration in shrimp Crangon affinis and in sea urchin Strongylocentrotus nudus. When C. affinis, which was kept in 50% sea water for one week, was transferred to 0, 25, 75 and 100% sea water and analyzed the concentration of DL-alanine. D-Ala changed more intensely than L-ala under both low and high salinity conditions.