Bieza Silvina A, Boubeta Fernando, Feis Alessandro, Smulevich Giulietta, Estrin Darío A, Boechi Leonardo, Bari Sara E
Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires Ciudad Universitaria , Buenos Aires C1428EHA, Argentina.
Inorg Chem. 2015 Jan 20;54(2):527-33. doi: 10.1021/ic502294z. Epub 2014 Dec 24.
The reactivity of inorganic sulfide species toward heme peptides was explored under biorelevant conditions in order to unravel the molecular details of the reactivity of the endogenous hydrogen sulfide toward heme proteins. Unlike ferric porphyrinates, which are reduced by inorganic sulfide, some heme proteins can form stable Fe(III)-sulfide adducts. To isolate the protein factors ruling the redox chemistry, we used as a system model, the undecapeptide microperoxidase (MP11), a heme peptide derived from cytochrome c proteolysis that retains the proximal histidine bound to the Fe(III) atom. Upon addition of gaseous hydrogen sulfide (H2S) at pH 6.8, the UV-vis spectra of MP11 closely resembled those of the low-spin ferric hydroxo complex (only attained at an alkaline pH) and cysteine or alkylthiol derivatives, suggesting that the Fe(III) reduction was prevented. The low-frequency region of the resonance Raman spectrum revealed the presence of an Fe(III)-S band at 366 cm(-1) and the general features of a low-spin hexacoordinated heme. Anhydrous sodium sulfide (Na2S) was the source of sulfide of choice for the kinetic evaluation of the process. Theoretical calculations showed no distal stabilization mechanisms for bound sulfide species in MP11, highlighting a key role of the proximal histidine for the stabilization of the Fe(III)-S adducts of heme compounds devoid of distal counterparts, which is significant with regard to the biochemical reactivity of endogenous hydrogen sulfide.
为了阐明内源性硫化氢与血红素蛋白反应的分子细节，我们在生物相关条件下研究了无机硫化物对血红素肽的反应活性。与能被无机硫化物还原的铁卟啉不同，一些血红素蛋白能形成稳定的Fe(III)-硫化物加合物。为了分离决定氧化还原化学性质的蛋白质因子，我们使用十一肽微过氧化物酶（MP11）作为系统模型，它是一种源自细胞色素c蛋白水解的血红素肽，保留了与Fe(III)原子结合的近端组氨酸。在pH 6.8下加入气态硫化氢（H₂S）后，MP11的紫外可见光谱与低自旋铁羟基配合物（仅在碱性pH下才能得到）以及半胱氨酸或烷基硫醇衍生物的光谱非常相似，这表明Fe(III)的还原受到了抑制。共振拉曼光谱的低频区域显示在366 cm⁻¹处存在一个Fe(III)-S带以及低自旋六配位血红素的一般特征。无水硫化钠（Na₂S）是该过程动力学评估中首选的硫化物来源。理论计算表明，MP11中结合的硫化物物种不存在远端稳定机制，这突出了近端组氨酸对于缺乏远端对应物的血红素化合物的Fe(III)-S加合物稳定化的关键作用，这对于内源性硫化氢的生化反应性具有重要意义。
