Hydrogen peroxide fluxes and compartmentalization inside growing Escherichia coli
Hydrogen peroxide fluxes and compartmentalization inside growing Escherichia coli
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DOI：
10.1128/jb.183.24.7182-7189.2001
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发表时间：
2001-12-01
影响因子：
3.2
通讯作者：
Imlay, JA
中科院分区：
文献类型：
--
作者：
Seaver, LC;Imlay, JA
当大肠杆菌在葡萄糖培养基中呈指数生长时，每秒产生约 14 muM 过氧化氢 (H2O2)。 H2O2 的稳态细胞内浓度取决于清除酶和细胞外流消散 H2O2 的速率。对两种主要清除酶（烷基氢过氧化物还原酶和过氧化氢酶）降解 H2O2 的速率进行了定量。为了估计流出速率，测定了膜对 H2O2 的渗透系数。系数为1.6 x 10(-3) cm/s，表明渗透性很大但不是无限的。这些数据允许计算内部 H2O2 通量和浓度。在这些生长条件下，Ahp 清除大部分内源性 H2O2，其中一小部分被过氧化氢酶降解，并且几乎没有任何物质能够持续足够长的时间来穿透细胞膜并离开细胞。强大的清除活性使葡萄糖生长的细胞内的 H2O2 浓度保持在 < 10(-7) M，远低于毒性明显的水平 (10(-6) M)。当细胞外的 H2O2 存在时，它进入细胞的速度会很快，但内部浓度可能仍比外部低一个数量级。这种梯度的存在在实验中得到了证实，这些实验揭示了共培养的清除剂缺陷突变体中不同程度的氧化应激。膜对 H2O2 的有限渗透性使清除系统的划分合理化，并预测分泌氧化还原循环药物的细菌不会经历与它们的竞争对手相同的 H2O2 剂量。
Escherichia coli generates about 14 muM hydrogen peroxide (H2O2) per s when it grows exponentially in glucose medium. The steady-state intracellular concentration of H2O2, depends on the rates at which this H2O2 is dissipated by scavenging enzymes and by efflux from the cell. The rates of H2O2 degradation by the two major scavenging enzymes, alkyl hydroperoxide reductase, and catalase, were quantified. In order to estimate the rate of efflux the permeability coefficient of membranes for H2O2 was determined. The coefficient is 1.6 x 10(-3) cm/s, indicating that permeability is substantial but not unlimited. These data allowed internal H2O2 fluxes and concentrations to be calculated. Under these growth conditions, Ahp scavenges the majority of the endogenous H2O2, with a small fraction degraded by catalase and virtually none persisting long enough to penetrate the membrane and exit the cell. The robust scavenging activity maintains the H2O2 concentration inside glucose-grown cells at < 10(-7) M, substantially below the level (10(-6) M) at which toxicity is evident. When extracellular H2O2 is present, its flux into the cell can be rapid, but the internal concentration may still be an order of magnitude lower than that outside. The presence of such gradients was confirmed in experiments that revealed different degrees of oxidative stress in cocultured scavenger-deficient mutants. The limited permeability of membranes to H2O2 rationalizes the compartmentalization of scavenging systems and predicts that bacteria that excrete redox-cycling drugs do not experience the same H2O2 dose that they impose on their competitors.