Physiological function of free D-alanine as an iso-osmotic effector in crustaceans

对克氏原螯虾、德氏全爪蟹和海岸长毛半笔石蟹在海水驯化过程中不同组织中游离D-和L-氨基酸的含量进行了测定，结果表明，随着高渗胁迫的沿着，这些甲壳动物肌肉和其他组织中的游离氨基酸含量增加。几个D-氨基酸中发现的组织，只有D-丙氨酸海水驯化过程中显着增加。D-丙氨酸占总丙氨酸的比例在海水中也增加到约50%。这些数据清楚地表明，D-丙氨酸是维持这些甲壳动物的组织等渗透压的主要的生物效应器。绒螯蟹Eriocheir Escherichia coli，在秋季产卵期间向下游迁移，在夏季之前的海水驯化期间，没有显示出明显的游离氨基酸和D-丙氨酸的增加。从夏季到秋季采集的中华绒螯蟹各组织中D-丙氨酸含量明显高于从春季到夏季采集的中华绒螯蟹。在夏季后的海水驯化过程中，该物种的D-丙氨酸的增加是高的，达到几乎相同的水平，在自然迁移的个人在海边捕获。海水驯化过程中，血淋巴中无机离子含量增加，游离氨基酸和甜菜碱含量无明显变化。因此，这些数据表明，只有无机离子负责血淋巴中的渗透调节，但D-丙氨酸以及其他几种氨基酸也负责高达45%的总渗透调节该物种的组织等渗在下游产卵migration.In这项研究中，D-丙氨酸在甲壳动物的组织中的生理功能被阐明作为一个主要的等渗效应。还已知小龙虾肌肉中的D-丙氨酸水平即使在海水中饥饿后和肌肉中施用D-或L-丙氨酸后也能维持。

Free D- and L-amino acids were determined on the various tissues of crayfish Porcambarus clarkii, marsh crab Holometopus dehaani, and shore crab Hemigrapsus penicillatus during seawater acclimation from freshwater.Along with the hyper-osmotic stress, several free amino acids increased in the muscle as well as the other tissues of these crustaceans. Of several D-amino acids found in the tissues, only D-alanine increased significantly during seawater acclimation. The ratio of D-alanine to total alanine also increased to about 50% in seawater. These data clearly indicate that D-alanine is a major osmo-effector for maintaining the tissue iso-osmotic pressure in these crustaceans.Woolly-handed crab Eriocheir japonicus, which migrates downstream during spawning in fall, did not show clear increase of free amino acids and D-alanine during seawater acclimation before summer. D-Alanine in the tissues of this crab is much higher in the individuals obtained from summer to fall than those from spring to summer. During seawater acclimation of this species obtained after summer, the increase of D-alanine was high and reached to almost the same level as that in naturally migrated individuals captured at seashore. During seawater acclimation, hemolymph showed the increase of only inorganic ions and no change of free amino acids and betaines. Thus, these data indicate that only inorganic ions are responsible for the osmotic regulation in hemolymph but D-alanine as well as other several amino acids are also responsible up to 45% of total osmolytes for the tissue iso-osmotic regulation of this species during downstream spawning migration.In this study, the physiological function of D-alanine in the tissues of crustaceans was elucidated to be as a major iso-osmotic effector. The level of D-alanine in the muscle of crayfish was also known to be maintained even after starvation in seawater and after administration of D- or L-alanine in the muscle.