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Abstract：
The hypothesis was tested that a kinetical flow equilibrium of uptake and efflux reactions is responsible for balancing the cellular zinc content. The experiments were done with the metal-resistant bacterium Cupriavidus metallidurans. In pulse-chase experiments, the cells were loaded with radioactive 65Zn and chased with the 100-fold concentration of non-radioactive zinc chloride. In parallel, the cells were loaded with isotope-enriched stable 67Zn and chased with non-enriched zinc to differentiate between zinc pools in the cell. The experiments demonstrated the existence of a kinetical flow equilibrium, resulting in a constant turnover of cell-bound zinc ions. The absence of the metal-binding cytoplasmic components, polyphosphate and glutathione, metal uptake, and metal efflux systems influenced the flow equilibrium. The experiments also revealed that not all zinc uptake and efflux systems are known in C. metallidurans. Cultivation of the cells under zinc-replete, zinc-, and zinc-magnesium-starvation conditions influenced zinc import and export rates. Here, magnesium starvation had a stronger influence compared to zinc starvation. Other metal cations, especially cobalt, affected the cellular zinc pools and zinc export during the chase reaction. In summary, the experiments with 65Zn and 67Zn demonstrated a constant turnover of cell-bound zinc. This indicated that simultaneously occurring import and export reactions in combination with cytoplasmic metal-binding components resulted in a kinetical flow equilibrium that was responsible for the adjustment of the cellular zinc content.
Understanding the biochemical action of a single enzyme or transport protein is the pre-requisite to obtain insight into its cellular function but this is only one half of the coin. The other side concerns the question of how central metabolic functions of a cell emerge from the interplay of different proteins and other macromolecules. This paper demonstrates that a flow equilibrium of zinc uptake and efflux reactions is at the core of cellular zinc homeostasis and identifies the most important contributors to this flow equilibrium: the uptake and efflux systems and metal-binding components of the cytoplasm.
Understanding the biochemical action of a single enzyme or transport protein is the pre-requisite to obtain insight into its cellular function but this is only one half of the coin. The other side concerns the question of how central metabolic functions of a cell emerge from the interplay of different proteins and other macromolecules. This paper demonstrates that a flow equilibrium of zinc uptake and efflux reactions is at the core of cellular zinc homeostasis and identifies the most important contributors to this flow equilibrium: the uptake and efflux systems and metal-binding components of the cytoplasm.
摘要：
测试了该假设，即吸收和流出反应的动力学流动平衡负责平衡细胞锌含量。实验是用耐金属细菌Cupriavidusmetallidurans进行的。在脉冲追踪实验中,细胞装载放射性65Zn，并用100倍浓度的非放射性氯化锌追踪。并行,细胞加载同位素富集的稳定67Zn，并用非富集锌追踪以区分细胞中的锌池。实验证明了动力学流动平衡的存在，导致细胞结合的锌离子不断周转。没有金属结合的细胞质成分，多磷酸盐和谷胱甘肽，金属吸收，金属外排系统影响了流动平衡。实验还表明，并非所有的锌吸收和流出系统都是已知的。在锌充足的情况下培养细胞，锌-,锌-镁-饥饿条件影响锌的进出口率。这里,与锌饥饿相比，镁饥饿的影响更大。其他金属阳离子，尤其是钴，在追逐反应过程中影响了细胞锌池和锌出口。总之,65Zn和67Zn的实验证明了细胞结合锌的恒定更新。这表明，与细胞质金属结合成分同时发生的输入和输出反应会导致动力学流动平衡，从而调节细胞锌含量。
目的：了解单一酶或转运蛋白的生化作用是了解其细胞功能的先决条件，但这只是其中的一半。另一方面涉及细胞的中心代谢功能如何从不同蛋白质和其他大分子的相互作用中出现的问题。本文证明了锌吸收和流出反应的流动平衡是细胞锌稳态的核心，并确定了这种流动平衡的最重要因素：吸收和流出系统以及细胞质的金属结合成分。
目的：了解单一酶或转运蛋白的生化作用是了解其细胞功能的先决条件，但这只是其中的一半。另一方面涉及细胞的中心代谢功能如何从不同蛋白质和其他大分子的相互作用中出现的问题。本文证明了锌吸收和流出反应的流动平衡是细胞锌稳态的核心，并确定了这种流动平衡的最重要因素：吸收和流出系统以及细胞质的金属结合成分。
