BIOSYNTHESIS OF VITAMIN B12 AND ANAEROBIC METABOLISM

维生素 B12 的生物合成和无氧代谢

• 批准号: 2177582
• 负责人: JOHN R ROTH
• 金额: $ 14.2万
• 依托单位: UNIVERSITY OF UTAH
• 依托单位国家: 美国
• 财政年份: 1985
• 资助国家: 美国
• 起止时间: 1985-07-01 至 1995-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2177582
• 关键词: Salmonella typhimurium; anaerobic bacteria; anaerobiosis; bacterial genetics; cobalt; ethanolamines; gene complementation; gene expression; gene induction /repression; genetic mapping; genetic promoter element; genetic transcription; microorganism metabolism; molecular cloning; mutagens; mutant; nitrogen; nucleic acid sequence; nutrition related tag; open reading frames; operon; point mutation; protein engineering; regulatory gene; vitamin B12; vitamin B12 coenzyme; vitamin biosynthesis

Cobalamin (B-12) is an essential nutrient for humans that is only synthesized by microbes and some protists. The biosynthesis of B-12 is rather poorly understood. The complexity and instability of intermediates has made biochemical approaches difficult and most study has been focused on bacteria with very poor genetic systems. We have found that the genetic organism, Salmonella typhimurium, is able to synthesize B-12 de novo when grown under anaerobic conditions. We have initiated a primarily genetic approach to the synthesis of B-12 and how that synthesis is regulated. We hope to identify the structural genes for all of the synthetic enzymes and elucidate the mechanisms whereby these genes are regulated in response to the end product (probably adenosylcobalamin), cAMP, and redox state of the cell. Synthesis, transport, and recycling of B-12 appears to require about 1% of the Salmonella genome. Despite the size of this genetic investment in B- 12, only four enzymes are known in Salmonella that require B-12 as a cofactor; none of these functions appears to be fundamentally important. The B-12 dependent functions include on (of two) routes to methionine, synthesis of a nonessential tRNA modification, and ability to use ethanolamine and propanediol as carbon sources. Which of these, or what undiscovered function, accounts for the importance of B-12 to Salmonella? Why does Salmonella synthesize B-12 only under anaerobic conditions? (Many obligate aerobes are known to be able to synthesize B-12.) What physiological factors account for the distribution of B-12 in nature? (It is absent from plants, required by animals and some protists, and synthesized primarily by microbes.) To approach questions of biological significance of B-12, we will investigate the anaerobic metabolism of Salmonella. Despite the great interest that has been focused on genetics and metabolism of Salmonella and its relative E. coli, anaerobic behavior has received rather little attention. We have to contribute to a better understanding of anaerobic metabolism and its regulation, with special attention to the role of B-12.

钴胺素（B-12）是人类的必需营养素 由微生物和一些生物合成。 B-12的生物合成是 相当理解。 中间体的复杂性和不稳定 使生化方法变得困难，大多数研究都集中在 在遗传系统非常差的细菌上。 我们发现遗传 有机体，沙门氏菌鼠伤寒，能够合成从头开始的B-12 在厌氧条件下生长。 我们已经启动了主要的遗传 B-12的合成以及如何调节该合成的方法。 我们 希望确定所有合成酶的结构基因和 阐明这些基因受到调节的机制 最终产物（可能是腺苷泡），营地和氧化还原状态 细胞。 B-12的合成，运输和回收似乎需要约1％ 沙门氏菌基因组。 尽管这种基因投资在B- 12，在沙门氏菌中只有四种酶，需要B-12作为A 辅助因子；这些功能似乎没有根本重要。 B-12依赖性功能包括在（两个）甲硫氨酸的路线上 非必需tRNA修饰的合成和使用的能力 乙醇胺和丙二醇作为碳源。 其中哪个，或什么 未发现的功能，说明了B-12对沙门氏菌的重要性？ 为什么仅在厌氧条件下，沙门氏菌才能合成B-12？ （许多 众所周知，强氧可以合成B-12。 生理因素解释了B-12在本质上的分布？ （它 动物和一些生物学家所要求的植物不存在，以及 主要由微生物合成。） 为了解决B-12生物学意义的问题，我们将 研究沙门氏菌的厌氧代谢。 尽管很棒 一直关注沙门氏菌和代谢的兴趣 它的相对大肠杆菌，厌氧行为几乎没有 注意力。 我们必须为更好地理解厌氧代谢和 它的调节，特别注意B-12的作用。