雨生红球藻合成虾青素过程中分泌铵离子的研究

Study on concomitant NH_4^+ secretion during astaxanthin synthesis inHaematococcus pluvialis

雨生红球藻在在缺氮(NF)的条件下,随着虾青素的合成,肽链内切酶(EP)的活性上升而蛋白质含量下降,天冬酰氨酸含量在前4天增加然后又减少,铵离子浓度则持续上升。相比之下,在氮充足(NR)的培养液中,藻细胞不合成虾青素,蛋白质和天冬酰氨酸的含量以及EP的活性基本稳定,培养液中也没有检测到铵离子。上述结果表明:①降解的蛋白质为虾青素的合成提供了碳源,②EP参与了蛋白质的降解反应,③为避免铵离子的毒害作用,蛋白质降解所产生的部分氨临时贮存在天冬酰氨酸中,而其余的则分泌到细胞外。

With the onset of astaxanthin synthesis in Haematococcus plwialis under the nitrogen-free condition （NF）, Endopeptidase （EP） activities increased along with the decreasing of protein. Asparagine rose significantly during the first 4 days, but decreased after that time. While, ammonium concentration in the broth increased continuously through out the cultivation period. By contrast, in nitrogen-repletion culture （NR）,the contents of protein and asparagine as well as EP activity maintained relatively constant, no astaxanthin and extracellular ammonium were detected. These results strongly suggest that： ①the degraded protein served as carbon source, to some extent, for the biosynthesis of astaxanthin; ② endopeptidase was involved in the degradative process; ③for detoxification, part of the ammonium generated by the protein degradation was transiently stored in asparagine, while the rest of which was expelled into the culture broth.