La Mar G N, Chatfield M J, Peyton D H, de Ropp J S, Smith W S, Krishnamoorthi R, Satterlee J D, Erman J E
Department of Chemistry, University of California, Davis 95616.
Biochim Biophys Acta. 1988 Oct 12;956(3):267-76. doi: 10.1016/0167-4838(88)90143-4.
The influence of solvent isotope composition on 1H-NMR resonance position and linewidth of heme methyls has been investigated for a variety of high-spin ferric hemoproteins for the purpose of detecting hydrogen-bonding interactions in the heme cavity. Consistently larger hyperfine shifts and paramagnetic linewidths in 2H2O than 1H2O are observed for metmyoglobins and methemoglobin possessing a coordinated water molecule. The analysis of the dynamics of labile proton exchange in sperm whale metmyoglobin, and the absence of any isotope effects in the five-coordinate Aplysia metmyoglobin, indicate that the significant axial modulation of heme electronic structure by solvent isotope is consistent with arising from distal hydrogen-bonding interactions. The presence or absence of similarly large isotope effects on shifts and linewidths in other hemoproteins, depending on the presence of a bound water in the distal heme pocket, suggests that this isotope effect can serve as a probe for the presence of such bound water. The absence of any detectable isotope effect on either shifts or linewidths in resting-state horseradish peroxidase supports a five-coordinate structure with bound water absent from the vicinity of the iron.
为了检测血红素腔内的氢键相互作用，研究了溶剂同位素组成对多种高自旋铁血红素蛋白中血红素甲基的1H-NMR共振位置和线宽的影响。对于具有配位水分子的高铁肌红蛋白和高铁血红蛋白，在2H2O中观察到的超精细位移和顺磁线宽始终比在1H2O中更大。对抹香鲸高铁肌红蛋白中不稳定质子交换动力学的分析，以及五配位海兔高铁肌红蛋白中不存在任何同位素效应，表明溶剂同位素对血红素电子结构的显著轴向调制与远端氢键相互作用引起的一致。其他血红素蛋白中位移和线宽是否存在类似的大同位素效应，取决于远端血红素口袋中是否存在结合水，这表明这种同位素效应可作为此类结合水存在的探针。静息态辣根过氧化物酶的位移或线宽均未检测到任何同位素效应，这支持了一种五配位结构，其中铁附近不存在结合水。
