Iron is an essential transition metal species for all living organisms and plays various physiologically important roles on the basis of its redox activity; accordingly, the disruption of iron homeostasis triggers oxidative stress and cellular damage. Therefore, cells have developed sophisticated iron-uptake machinery to acquire iron while protecting cells from uncontrolled oxidative damage during the uptake process. To examine the detailed mechanism of iron uptake while controlling the redox status, it is necessary to develop useful methods with redox state selectivity, sensitivity, and organelle specificity to monitor labile iron, which is weakly bound to subcellular ligands. Here, we report the development of Mem-RhoNox to monitor local Fe(II) at the surface of the plasma membrane of living cells. The redox state-selective fluorescence response of the probe relies on our recently developed N-oxide strategy, which is applicable to fluorophores with dialkylarylamine in their π-conjugation systems. Mem-RhoNox consists of the N-oxygenated rhodamine scaffold, which has two arms, both of which are tethered with palmitoyl groups as membrane-anchoring domains. In an aqueous buffer, Ac-RhoNox, a model compound of Mem-RhoNox, shows a fluorescence turn-on response to the Fe(II) redox state-selectively. An imaging study with Mem-RhoNox and its derivatives reveals that labile Fe(II) is transiently generated during the major iron-uptake pathways: endocytotic uptake and direct transport. Furthermore, Mem-RhoNox is capable of monitoring endosomal Fe(II) in primary cultured neurons during endocytotic uptake. This report is the first example that identifies the generation of Fe(II) over the course of cellular iron-uptake processes.

中文翻译：

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通过膜锚定Fe（II）荧光探针可视化铁的胞吞摄取过程中的Fe（II）离子释放

铁是所有活生物体必不可少的过渡金属物种，并基于其氧化还原活性发挥各种生理重要作用。因此，铁稳态的破坏触发了氧化应激和细胞损伤。因此，细胞已开发出先进的铁吸收机制，以获取铁，同时保护细胞在吸收过程中不受不受控制的氧化损伤。为了研究控制氧化还原状态时铁摄取的详细机制，有必要开发具有氧化还原状态选择性，敏感性和细胞器特异性的有用方法，以监测与亚细胞配体弱结合的不稳定铁。在这里，我们报告Mem-RhoNox的发展，以监测活细胞质膜表面的局部Fe（II）。N-氧化物策略，适用于在其π-共轭体系中具有二烷基芳基胺的荧光团。Mem-RhoNox由N组成-氧氧化罗丹明支架，具有两个臂，两个臂都与棕榈酰基团拴在一起作为膜固定结构域。在水性缓冲液中，Mem-RhoNox的模型化合物Ac-RhoNox显示出对Fe（II）氧化还原状态选择性的荧光开启响应。用Mem-RhoNox及其衍生物进行的影像学研究表明，不稳定的Fe（II）在主要的铁吸收途径（细胞吞噬和直接转运）过程中短暂产生。此外，Mem-RhoNox能够监测内吞摄取过程中原代培养神经元的内体Fe（II）。该报告是鉴定细胞铁摄取过程中Fe（II）生成的第一个例子。