林肯链霉菌林肯变种谷氨酰胺合成酶的研究(英文)

Studies on Glutamine Synthetase from Streptomyces lincolnensis var. Lincolnensis

林肯链霉菌林肯变种是林可霉素的产生菌，研究中发现其菌丝体中谷氨酰胺合成酶（ Ｇ Ｓ）的比活力与林可霉素的生物合成存在正相关性．在此基础上，报道了 Ｇ Ｓ的分离纯化、分子特征、酶学性质和活力调节特性．采用硫酸铵分级沉淀、 Ｄ Ｅ５２ 离子交换层析、 Ｓｅｐｈａｒｏｓｅ ６ Ｂ凝胶过滤等方法，从林肯链霉菌林肯变种中分离纯化了 Ｇ Ｓ，用聚丙烯酰胺凝胶电泳（ Ｐ Ａ Ｇ Ｅ）鉴定为单一组分．以梯度 Ｐ Ａ Ｇ Ｅ 和凝胶过滤法测得 Ｇ Ｓ的相对分子质量为 ６６０ ０００， Ｓ Ｄ Ｓ Ｐ Ａ Ｇ Ｅ测得其亚基相对分子质量为５５ ０００，表明该酶由 １２ 个相同的亚基构成． Ｍｇ２＋ 或 Ｍｎ２＋ 作为辅助因子对 Ｇ Ｓ的催化活性是必需的．反馈抑制是 Ｇ Ｓ的一种重要调节方式，这种抑制作用是以累积的方式进行的，这表明各种代谢物对 Ｇ Ｓ的作用位点不同，它们对 Ｇ Ｓ的抑制作用是相互独立的．以受腺苷化去腺苷化调节的产气克雷伯氏菌 Ｇ Ｓ作对照，研究发现林肯链霉菌林肯变种 Ｇ Ｓ没有明显的氨休克作用，且经蛇毒磷酸二酯酶处理后，其活力没有变化．这些结果都说明林肯链霉菌林肯变种 Ｇ Ｓ不存在腺苷化共价修饰这一调节方式．另外，对不同氮源生长条件下林肯链霉菌林肯变种无细?

Streptomyces lincolnensis var. lincolnensis produces lincomycin. It has been found that there is a positive correlation between the specific activity of mycelial glutamine synthetase (GS) and lincomycin biosynthesis. In present paper,the purification,characteristics and regulatory properties of GS are reported. The Mr of the native enzyme is approximately 660 000 and it is composed of 12 identical subunits,each of Mr 55 000. Mg 2+ or Mn 2+ is absolutely needed as a cofactor for GS activity. The enzyme activity is regulated through feedback inhibition and cumulative feedback inhibition. However,it can not be regulated by the covalent modification,adenylylation and deadenylylation. Interestingly,the enzyme activity is not influenced by ammonia shock or snake venom phosphodiesterase treatment,while the activity of GS from K. aerogenes is remarkably changed under these conditions. The results obtained suggest that there is no evidence for enzymatic adenylylation of glutamine synthetase from Streptomyces lincolnensis var. lincolnensis.Abstract Streptomyces lincolnensis var. lincolnensis produces lincomycin. It has been found that there is a positive correlation between the specific activity of mycelial glutamine synthetase (GS) and lincomycin biosynthesis. In present paper,the purification,characteristics and regulatory properties of GS are reported. The Mr of the native enzyme is approximately 660 000 and it is composed of 12 identical subunits,each of Mr 55 000. Mg 2+ or Mn 2+ is absolutely needed as a cofactor for GS activity. The enzyme activity is regulated through feedback inhibition and cumulative feedback inhibition. However,it can not be regulated by the covalent modification,adenylylation and deadenylylation. Interestingly,the enzyme activity is not influenced by ammonia shock or snake venom phosphodiesterase treatment,while the activity of GS from K. aerogenes is remarkably changed under these conditions. The results obtained suggest that there is no evidence for enzymatic adenylylation of glutamine synthetase from Streptomyces lincolnensis var. lincolnensis.