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

传统上，人们一直认为d -氨基酸不存在于高等生物的游离氨基酸池或蛋白质中。结果表明，甲壳纲双壳类中d -丙氨酸含量较高，其他双壳类、腹足类和头足类中含量较低。本研究旨在进一步了解d -丙氨酸在双壳类动物中的分布及其生理作用。1)研究了用精-l -半胱氨酸-组微米-phalaldehyde预标记D和l -丙氨酸的改进HPLC测定方法。2)测定了海生双壳类Barnea dilatata和淡水双壳类Unio douglasiae和Anodonta woodiana的组织中d -丙氨酸的含量，这两种双壳类属于Eulamellibranchia亚纲。D-丙胺在扩张巴尔鱼肌肉和内脏中含量较高，D/D+L比值分别为0.4和0.5。另一方面，道格拉斯花楸和木犀草组织中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) 30只硬蛤在人工海水（35%、100%）中驯化2 d。7天后，使用人工海水盐混合物将养殖水的盐度逐渐提高到53%（150%海水）。100%和150%标本组织中分别测定D和l -丙氨酸。100%标本内收肌、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 -丙氨酸含量分别增加到45.6、15.1和13.1 μ mol/g。150%的海水标本各组织中l -丙氨酸含量均升高。这些结果表明d -丙氨酸和l -丙氨酸是硬蛤渗透调节的渗透分子。

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.