Imlay J A, Fridovich I
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710.
J Bacteriol. 1992 Feb;174(3):953-61. doi: 10.1128/jb.174.3.953-961.1992.
Mutants of Escherichia coli that are devoid of superoxide dismutase (SOD) fail to grow in aerobic minimal medium. This is largely because of the O2- sensitivities of several amino acid biosynthetic pathways, since amino acid supplements can restore growth, albeit at a slow rate. We now report that growth in amino acid-supplemented medium can be further stimulated by the presence of extracellular osmolytes. Osmolytes also partially suppress the amino acid requirements of the SOD mutant. These data suggest that the combination of oxidative injury and turgor pressure permeabilizes the cell envelope and that critical metabolites, including the limiting products of damaged biosynthetic pathways, escape from the cell. External osmolytes may offer protection by countervailing the usual turgor pressure and thus stabilizing the damaged envelope. This model is consistent with the previous observation that deficiency of cell wall components is lethal to SOD mutants. A pseudorevertant that can grow at a moderate rate in normosmotic medium without amino acid supplementation has been obtained (J. A. Imlay and I. Fridovich, Mol. Gen. Genet. 228:410-416, 1991). Analysis suggests that the suppressor mutation allows the envelope either to resist or to tolerate oxidative lesions. Study of the pseudorevertant may illuminate the molecular basis of this oxidative envelope injury.
缺乏超氧化物歧化酶（SOD）的大肠杆菌突变体无法在有氧基本培养基中生长。这主要是由于几种氨基酸生物合成途径对超氧阴离子（O₂⁻）敏感，因为添加氨基酸可以恢复生长，尽管速度较慢。我们现在报告，细胞外渗透溶质的存在可以进一步刺激在添加氨基酸的培养基中的生长。渗透溶质还部分抑制了SOD突变体对氨基酸的需求。这些数据表明，氧化损伤和膨压的共同作用使细胞膜通透性增加，包括受损生物合成途径的限制性产物在内的关键代谢物从细胞中逸出。外部渗透溶质可能通过抵消通常的膨压从而稳定受损的细胞膜来提供保护。该模型与先前观察到的细胞壁成分缺乏对SOD突变体是致命的这一现象一致。已经获得了一种假回复突变体，它可以在等渗培养基中以中等速度生长而无需添加氨基酸（J.A. 伊姆利和I. 弗里多维奇，《分子与普通遗传学》228:410 - 416, 1991）。分析表明，抑制突变使细胞膜能够抵抗或耐受氧化损伤。对假回复突变体的研究可能会阐明这种氧化细胞膜损伤的分子基础。
