...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Journal of bacteriology >A high-affinity cbb3-type cytochrome oxidase terminates the symbiosis-specific respiratory chain of Bradyrhizobium japonicum.
【24h】

A high-affinity cbb3-type cytochrome oxidase terminates the symbiosis-specific respiratory chain of Bradyrhizobium japonicum.

机译：高亲和力的cbb3型细胞色素氧化酶终止了日本根瘤菌的共生特异性呼吸链。

获取原文
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

It has been a long-standing hypothesis that the endosymbiotic rhizobia (bacteroids) cope with a concentration of 10 to 20 nM free O2 in legume root nodules by the use of a specialized respiratory electron transport chain terminating with an oxidase that ought to have a high affinity for O2. Previously, we suggested that the microaerobically and anaerobically induced fixNOQP operon of Bradyrhizobium japonicum might code for such a special oxidase. Here we report the biochemical characteristics of this terminal oxidase after a 27-fold enrichment from membranes of anaerobically grown B. japonicum wild-type cells. The purified oxidase has TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) oxidase activity as well as cytochrome c oxidase activity. N-terminal amino acid sequencing of its major constituent subunits confirmed that presence of the fixN,fixO, and fixP gene products. FixN is a highly hydrophobic, heme B-binding protein. FixO and FixP are membrane-anchored c-type cytochromes (apparent Mrs of 29,000 and 31,000, respectively), as shown by their peroxidase activities in sodium dodecyl sulfate-polyacrylamide gels. All oxidase properties are diagnostic for it to be a member of the cbb3-type subfamily of heme-copper oxidases. The FixP protein was immunologically detectable in membranes isolated from root nodule bacteroids, and 85% of the total cytochrome c oxidase activity in bacteroid membranes was contributed by the cbb3-type oxidase. The Km values for O2 of the purified enzyme and of membranes from different B. japonicum wild-type and mutant strains were determined by a spectrophotometric method with oxygenated soybean leghemoglobin as the sole O2 delivery system. The derived Km value for O2 of the cbb3-type oxidase in membranes was 7 nM, which is six- to eightfold lower than that determined for the aerobic aa3-type cytochrome c oxidase. We conclude that the cbb3-type oxidase supports microaerobic respiration in endosymbiotic bacteroids.
机译：长期存在的假说是，通过使用专门的呼吸电子转运链终止以氧化酶终止的内源性共生根瘤菌（类杆菌体）可解决豆科植物根瘤中浓度为10至20 nM的游离O2对O2的亲和力。以前，我们建议日本厌氧根瘤菌的厌氧和厌氧诱导的fixNOQP操纵子可能编码这种特殊的氧化酶。在这里，我们从厌氧生长的日本血吸虫野生型细胞膜上富集27倍后，报告了该末端氧化酶的生化特征。纯化的氧化酶具有TMPD（N，N，N'，N'-四甲基-对苯二胺）氧化酶活性以及细胞色素C氧化酶活性。其主要组成亚基的N端氨基酸测序证实了fixN，fixO和fixP基因产物的存在。 FixN是一种高度疏水的血红素B结合蛋白。 FixO和FixP是膜锚定的c型细胞色素（表观夫人分别为29,000和31,000），如它们在十二烷基硫酸钠-聚丙烯酰胺凝胶中的过氧化物酶活性所显示。所有的氧化酶特性都可以诊断为它是血红铜氧化酶cbb3型亚家族的成员。 FixP蛋白在从根结节类细菌分离的膜中可通过免疫学检测，而类细菌膜中总细胞色素C氧化酶活性的85％由cbb3型氧化酶贡献。通过分光光度法，用氧化大豆豆血红蛋白作为唯一的O2输送系统，测定纯化的酶和来自不同日本血吸虫野生型和突变株的膜的O2的Km值。膜中cbb3型氧化酶的O2推导Km值为7 nM，比有氧aa3型细胞色素c氧化酶测定的Km值低6至8倍。我们得出结论，cbb3型氧化酶支持内共生类细菌中的微氧呼吸。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号