Bis-histidyl hexacoordination in hemoglobins facilitates heme reduction kinetics.
Bis-histidyl hexacoordination in hemoglobins facilitates heme reduction kinetics.
复制标题
血红蛋白中的双组氨酰六配位促进血红素还原动力学。
DOI：
10.1021/ja046990w
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
Hargrove,MarkS
中科院分区：
文献类型：
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作者：
Weiland,TheodoreR;Kundu,Suman;Trent3rd,JamesT;Hoy,JulieA;Hargrove,MarkS
六配位血红蛋白是一类蛋白质，在保持与外源配体结合的能力的同时，显示出与血红素铁的可逆的双组氨酸配位。对它们生理功能的一种假设是，它们清除一氧化氮，这是一种氧化蛋白质的反应，需要还原血红素铁才能继续。六配位血红蛋白的还原动力学，包括人的脑红蛋白和细胞球蛋白，以及来自聚球藻和大米的那些，与肌红蛋白、大豆豆类血红蛋白和几个相关的突变蛋白进行了比较。在所有情况下，与五配位血红蛋白相比，双组氨酸配位大大提高了二亚硫酸钠的还原速度。在肌红蛋白和豆红蛋白中，还原受到电子转移速率常数的限制，而在六面体血红蛋白中，还原仅受还原剂的双分子结合限制。这些结果可以用六配位和五配位血红蛋白还原重组能的不同来解释。
Hexacoordinate hemoglobins are a class of proteins that exhibit reversible bis-histidyl coordination of the heme iron while retaining the ability to bind exogenous ligands. One hypothesis for their physiological function is that they scavenge nitric oxide, a reaction that oxidizes the protein and requires reduction of the heme iron to continue. Reduction kinetics of hexacoordinate hemoglobins, including human neuroglobin and cytoglobin, and those fromSynechocystisand rice, are compared to myoglobin, soybean leghemoglobin, and several relevant mutant proteins. In all cases, bis-histidyl coordination greatly increases the rate of reduction by sodium dithionite when compared to pentacoordinate hemoglobins. In myoglobin and leghemoglobin, reduction is limited by the rate constant for electron transfer, whereas in the hexacoordinate hemoglobins reduction is limited only by bimolecular binding of the reductant. These results can be explained by differences in the reorganization energy for reduction between hexacoordinate and pentacoordinate hemoglobins.