RESEARCH STUDY ON THE DISTRIBUTION OF D-AMINO ACIDS AND D-AMINO ACID RACEMASE IN MICROALGAE

测定了D-氨基酸在海洋硅藻和淡水微藻中的分布。以及不同培养条件下海星藻D-氨基酸含量的变化。被检查过了。此外，对微藻中D-氨基酸的来源进行了研究。在硅藻、海星藻、海链藻、菱形藻和拟菱形藻中发现了游离D-天冬氨酸和D-丙氨酸的存在。在淡水微藻、高山葡萄孢霉、小球藻、普通球藻和斜生栅藻中也发现了D-天冬氨酸，但这些物种中没有检测到D-丙氨酸。D-丙氨酸的含量随生长阶段的不同而不同：海星藻的D-丙氨酸含量。稳定期增加，消退期减少。经80%乙醇提取后的硅藻残渣中检测到D-天冬氨酸、D-谷氨酸和D-丙氨酸的结合形式，而在淡水微藻中未检测到D-丙氨酸。在海洋硅藻Thalassiosira sp.中检测到丙氨酸外消旋酶活性。它是无菌培养的。该酶的最适pH极高，约为9.5，底物L-丙氨酸的Km值为19.7 mM。该酶在反应中不需要吡哆醛5‘-磷酸(PLP)作为辅因子。这些结果表明海链霉菌的丙氨酸外消旋酶。与细菌酶相比，PLP作为辅因子与PLP结合得更紧密。

Distribution of free and combined D-amino acids in marine diatoms and freshwater microalgae was measured. And variation in D-amino acids content under various culture conditions of diatom, Asterionella sp. was examined. Furthermore, the origin of D-amino acids in microalgae was researched.1. The presence of free D-aspartate and D-alanine was verified in diatoms, Asterionella sp., Thalassiola sp., Nitzschia sp., and Pseudo-nitzschia sp. D-Aspartate was also found in fresh water microalgae, Botrydiopsos alpina, Chlorella pyeniodos, C.vulgaris and Scenedesumus obliquus, but D-alanine was not detected in these species.2. The content of D-alanine varied by growth phase : D-Alanine content of Asterionella sp. increased in stationary phase and decreased in extinction phase.3. Combined form of D-aspartate, D-glutamate and D-alanine were detected in the residue of diatoms after extracting with 80% ethanol, but D-alanine was not detected in freshwater microalgae.4. Alanine racemase activity was detected in the marine diatom, Thalassiosira sp. which was cultured germ-free. Optimal pH of this enzyme was extremely high, about 9.5 and the Km value (substrate L-alanine) was 19.7 mM. The enzyme did not require pyridoxal 5'-phosphate (PLP) as a cofactor in the reaction. These results suggest that alanine racemase from Thalassiosira sp. bindes PLP more tightly as a cofactor compared with bacterial enzyme.