期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 104, 期 22, 页码 9475-9480出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0703360104
关键词
ammonium assimilation; glutamine; metabolic circuit; suppressor
资金
- NIGMS NIH HHS [GM 38361, R37 GM038361, R01 GM038361] Funding Source: Medline
The central nitrogen metabolic circuit in enteric bacteria consists of three enzymes: glutamine synthetase, glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH). With the carbon skeleton provided by 2-oxoglutarate, ammonia/ammonium (NH4+) is assimilated into two central nitrogen intermediates, glutamate and glutamine. Although both serve as nitrogen donors for all biosynthetic needs, glutamate and glutamine play different roles. Internal glutamine serves as a sensor of external nitrogen availability, and its pool concentration decreases upon nitrogen limitation. A high glutamate pool concentration is required to maintain the internal K+ pool. The configuration of high glutamate and low glutamine pools was disrupted in GOGAT(-) mutants under low NH4+ conditions: the glutamate pool was low, the difference between glutamate and glutamine was diminished, and growth was defective. When a GOGAT- mutant was cultured in an NH(4)(+-)limited chemostat, two sequential spontaneous mutations occurred. Each resulted in a suppressor mutant that outgrew its predecessor in the chemostat. The first suppressor overexpressed GDH, and the second also had a partially impaired glutamine synthetase. The result was a triple mutant in which NH4+ was assimilated by two enzymes instead of the normal three! and yet glutamate and glutamine pools and growth were essentially normal. The results indicate preference for the usual ratio of glutamate and glutamine and the resilient and compensatory nature of the circuit on pool control. Analysis of other suppressor mutants selected on solid medium suggests that increased GDH expression is the key for rescue of the growth defect of GOGAT- mutants under low NH4+ conditions.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据