Studies on the D-alanine in the aquatic animals

最近，在许多水生动物中检测到高水平的D-丙氨酸，但关于游离D-丙氨酸积累的生化机制还知之甚少。为进一步了解D-丙氨酸在水生动物体内的分布规律，对日本对虾蜕皮周期中尾肌肉80%乙醇提取物中D-丙氨酸和L-丙氨酸等氨基酸进行了分析。虽然D-丙氨酸与总丙氨酸的浓度比(D/D+L)与蜕皮周期相同，但所有受试对虾尾肌中的总丙氨酸水平都在4~20μ/g之间。检测到大量甘氨酸，含量分别为87~195mol.moL/g。牛磺酸和丙氨酸在无脊椎动物中含量丰富，但相对较低。2 2 5~3 2 4μ/g的游离氨基酸总量增加。谷氨酰胺、丙氨酸和精氨酸在未蜕皮的对虾中也有所增加。以L丙氨酸和D-丙氨酸为底物，测定了中国对虾肝脏和卵巢中的丙氨酸外消旋酶活性。所有标本的肝脏中均有D-to-L方向的活性。活性最强的是Taklfugu poecilonotus和Taklfugu poecilonotus。红色毛滴虫卵巢中只有D-对L方向的丙氨酸消旋酶活性较弱，而红色毛滴虫卵巢则没有。这些结果表明河豚可以利用饲料中的D-丙氨酸残留物。

Recently, high levels of fee D-alanine were detected in the many aquatic animals, but a little information has been available about the biochemical mechanisms of free D-alanine accumulation. The present studies were planned to accumulate more information on the distribution of D-alanine in aquatic animals.D-and L-alanine and the other amino acids were analyzed in the 80% ethanol extracts from the tail muscles of cultured Kurum shrimp Penaeus japonicus during intermolt cycle. Total alanine levels were 4〜20 μmol/g in the tail muscles of all the shrimp analyzed, although concentration ratio of D-alanine to total alanine (D/D+L), which were 0.42〜0.47, were as the same as during intermolt cycle. Significant amount of glycine was detected, amounting to 87〜195μmol/g, respectively. Taurine and alanine, they are abundant in invertebrates, were comparatively lower. Total of free amino acids (225〜324μmol/g) increased in the premolt shrimps. Glutamine, prorine and argine also increased in the premolt shrimps. On the other hand, glycine increased in the postmolt shrimps.Alanine racemase activities were examined on the crude enzyme solutions from the liver and ovary of Takifugu poecllonotus, T. nlphobles, T. pardahs and T. rubrlpes, using L-alanine or D-alanine as substrates. The activity in the only D-to-L direction is found in liver of all specimens. The activity is most strong in T nlphobles, following Taklfugu poecilonotus and T. pardalis. The ovary of T. niphobles showed week activity of alanine racemase in only D-to-L direction, but not T. rubripes. These results suggest that puffers can use D-alanine remains in feed.