Dinitrosyl Iron Complexes in Chemistry and Biochemistry

雙亞硝基鐵化合物於化學與生物化學之研究

羅鳳君(Feng-Chun Lo)

指導教授 ： 廖文峯 ； 俞聖法

國立清華大學/理學院/化學系/博士(2008年)

摘要

雙亞硝基鐵硫化合物已被鑑定為內生性的一氧化氮衍生物,一般出現於一氧化氮過度產生的各種組織中。由於他們的反應性，雙亞硝基鐵硫化合物擁有許多重要的生物標的。一般而言，生物體內具有蛋白質鍵結的雙亞硝基鐵硫化合物和小分子量的雙亞硝基鐵硫化合物。小分子的雙亞硝基鐵硫化合物與一氧化碳氣體比較，其為較有效的亞硝基化試劑，可將蛋白質亞硝基化形成硫-亞硝基化蛋白質或蛋白質鍵結的雙亞硝基鐵硫化合物。其中，亞硝基化蛋白質可以導致蛋白質的結構改變進而調控許多重要的生理機制。
為瞭解小分子量的雙亞硝基鐵硫化合物之化學特性,我們合成了許多小分子量的雙亞硝基鐵硫化合物。除了解其化學與物理特性外,這些化合物也被實際地應用於生物系統中以研究是否與生物體內所產生的雙亞硝基鐵硫化合物有相同的生物功能。將小分子雙亞硝基鐵硫化合物與人類白血病K562細胞作用，實驗結果證實當其結合紫外線A時可抑制人類白血病K562細胞的生長。因此，小分子的雙一氧化氮含鐵錯化合物可當作一氧化氮供應劑提供一氧化氮至各種癌細胞。
此外，利用大腸桿菌細胞質中的轉錄因子SoxR與雙亞硝基鐵硫化合物作用來説明這些合成的雙亞硝基鐵硫化合物是否具有一氧化氮釋放或者轉移的特性。 由動力學的實驗顯示具有雙牙基硫醇配位的雙亞硝基鐵硫化合物不論在細菌體內或是蛋白質溶液中都具有相對地穩定性。而單牙基配位的雙亞硝基鐵硫化合物在水溶液中會形成反磁性的雙核Roussin’s red ester，此反磁性雙核化合物仍具有將一氧化氮轉移給SoxR蛋白質的能力。
除了研究小分子的雙亞硝基鐵硫化合物外,我們也同時研究在施以一氧化氮後所形成之蛋白質鍵結的雙亞硝基鐵硫錯化中心。利用X光吸收光譜來探討亞硝基化後SoxR蛋白質的鐵硫簇結構變化。實驗結果顯示，亞硝基化SoxR蛋白質會造成其鐵硫簇降解，進而蛋白質鍵結的雙亞硝基鐵硫化合物。此結果亦說明SoxR蛋白質在面臨氧化及硝化壓力時採用相當不同的活化機制來調控下游基因soxS的表現。

關鍵字

雙亞硝基化合物

並列摘要

Dinitrosyl iron complexes (DNICs) are endogenous nitric oxide derived species that can appear in various NO overproducing tissues. Due to their reactivity, they may appear as multiple biologically important targets. Two kinds of DNICs, protein-bound DNIC and low- molecular weight DNIC (LMW-DNIC), are existent. Alternatively, the LMW- DNICs are much more powerful nitrosative agents than NO. It can provide nitrosative modification of proteins, forming either protein-S-nitrosothiols or protein-bound DNICs. Nitrosylation of proteins can lead with the variations of protein function and may result in physiological significance for NO trafficking among the biological systems.
Here, several synthesized LMW-DNICs were applied to the biological system. They were investigated and we found that they represented similar properties as biological DNICs. Treating human erythroleukemia K562 cells with DNICs and UVA indicated DNIC can decrease the percentage survival. It implicates that LMW-DNICs may serve as a potentially nitric oxide donor reagent in pharmacological delivery of NO to various tumors.
To have a better understanding how the NO exchange occurred within the biological systems, we supplement with the recombinant SoxR protein either in vivo or in vitro to differentiate the interaction of synthetic DNICs by evaluating their NO-release or NO-transfer characteristics. The corresponding kinetics studies indicate the bi-dentate thiolate ligands maintain better stabilities of synthetic DNIC in vivo or in vitro whereas, the mono-dentate DNIC formed a diamagnetic dimeric Roussin’s red ester nitrosylated complexes in aqueous solution. The diamagnetic nitrosylated species is still sustainable to translocate the NO between dinitrosyl iron complexes and the SoxR proteins.
To elucidate the transcriptional insight mediated by SoxR protein, we have further employed X-ray absorption spectroscopy (XAS) methods to study the various states of SoxR including the nitrosylated one. The spectroscopic data derived from the CD, UV-vis, EPR, and XAS methods indicated that the [2Fe-2S] cluster of SoxR is actually degenerated by nitric oxide through the formation the protein-bound DNIC. The structural features of the oxidized one are quite different from the nitrosylated SoxR. On the basis of these, we have illustrated that the structural insights for transcriptional mechanisms might exhibits large discrepancies between these two active forms, oxidized and nitrosylated.

並列關鍵字

dinitrosyl iron complex

參考文獻

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