The studies on the mechanism of D-alanine accumulation in bivalves

传统上，人们认为D-氨基酸不存在于高等生物的游离氨基酸库或蛋白质中。结果表明，D-丙氨酸在真鳃亚纲的双壳类中含量较高，而在其它双壳类、腹足类和头足类中含量较低。本研究以双壳贝类为材料，采用乙酰半胱氨酸-omicron-phalaldehyde标记的高效液相色谱法（HPLC）测定D-丙氨酸和L-丙氨酸的含量，并对测定结果进行了分析，为进一步研究D-丙氨酸在双壳贝类体内的分布和生理作用奠定了基础本文测定了一种海洋双壳类动物Barnea damagata和两种淡水双壳类动物Unio douglasiae和Anodonta woodiana的组织中丙氨酸的含量，真瓣鳃亚纲鱼的肌肉和内脏中D-丙氨酸含量较高，D/D+L比值分别为0.4和0.5。道格拉斯蚌和背角无齿蚌组织中D-丙氨酸含量较低。D/D+L比值分别为0.22-0.47和0.05-0.27。3）将30只文蛤（Meretrix Iusoria）在人工海水（35%、100%海水）中驯化2d。7天后，使用人工海水盐混合物将饲养水中的盐度逐渐增加到53%（150%海水）。100%和150%的组织中检测到D和L-丙氨酸。闭壳肌、鳃和中肠腺中D-丙氨酸含量分别为29.4、7.3和3.0 μ mol/g。经150%海水驯化后，D-丙氨酸含量分别提高到45.6、15.1和13.1 μ mol/g。150%海水样品各组织中L-丙氨酸的含量均增加。这些结果表明，D-丙氨酸和L-丙氨酸一起是调节文蛤渗透压的渗透调节剂。

Traditionally, it has been assumed that D-amino acids are not present in the free amino acid pools or proteins of higher organisms. Author showed that the content of D-alanine is high level in bivalves belong to Subclass Eulamellibranchia and low level in other bivalves, gastropods and cephalopods. The present studies were planned to accumulate more information on distribution and physiological role of D-alanine in bivalves.1) Improved HPLC method for the determination of D and L-alanine pre-labeled with accety-L-cysteine-omicron-phalaldehyde was invetigated.2) The content of D-alanine was determined in the tissues of a marine bivalve Barnea dilatata and two species of fresh water bivalves Unio douglasiae and Anodonta woodiana which belog to Subclass Eulamellibranchia. D-alamine contents was high level in the muscle and viscera of Barnea dilatata and D/D+L ratio was 0.4 and 0.5, respectively. On the other hand, D-alanine content in the tissues of Unio douglasiae and Anodonta woodiana was low level. But D/D+L ratio was 0.22-0.47 and 0.05-0.27, respectively.3) Thirty specimens of hard clam Meretrix Iusoria were acclimated in the artificial seawater (35%, 100% seawater) for two days. After 7 days salinity in the rearing water was gradually increased to 53% (150% seawater) usingan artificial seawater salt mixture. D and L-alanine were deterined in the tissues of 100% and 150% specimens. The amounts of D-alanine in the adductor muscle, gills and mid-gut gland of 100% specimens were 29.4,7.3 and 3.0 mumol/g respectively. After acclimation of 150% seawater the contents of D-alanine were increased to 45.6,15.1 and 13.1 mumol/g, respectively. The content of L-alanine was also increased in all tissues of 150% seawater specimens. These results suggest that D-alanine together with L-alanine is the osmolyte for osmoregulation in hard clam.