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

测定了游离和结合d -氨基酸在海洋硅藻和淡水微藻中的分布。考察了不同培养条件下硅藻d -氨基酸含量的变化。并对微藻中d -氨基酸的来源进行了研究。在硅藻、Asterionella sp.、Thalassiola sp.、Nitzschia sp.和pseudonitzschia sp.中均检测到游离d -天冬氨酸和d -丙氨酸，在淡水微藻、Botrydiopsos alpina、pyeniochlorella、c.o vulgaris和Scenedesumus obliquus中也检测到d -天冬氨酸，但未检测到d -丙氨酸。d -丙氨酸含量随生长阶段的不同而变化，在静止期d -丙氨酸含量增加，在灭灭期d -丙氨酸含量减少。3 .硅藻残渣经80%乙醇提取后可检出d -天冬氨酸、d -谷氨酸和d -丙氨酸的组合形式，而淡水微藻中未检出d -丙氨酸。对无菌培养的海洋硅藻进行了丙氨酸消旋酶活性检测。该酶的最适pH约为9.5，Km值（底物l -丙氨酸）为19.7 mM。该酶在反应中不需要5′-磷酸吡多醛（PLP）作为辅助因子。这些结果表明，与细菌酶相比，海assiosira sp.的丙氨酸消旋酶作为辅助因子更紧密地结合PLP。

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.