La Mar G N, Budd D L, Viscio D B, Smith K M, Langry K C
Proc Natl Acad Sci U S A. 1978 Dec;75(12):5755-9. doi: 10.1073/pnas.75.12.5755.
A proton NMR method is described for determining the orientation of a porphyrin within the heme pocket of a hemoprotein. The pattern of the hyperfine-shifted heme methyl resonances in low-spin ferric model compounds is demonstrated to characteristically reflect the position of a localized low-symmetry perturbation on the pi system. The specific assignments via deuteration of the two interconvertible sets of methyl resonances observed for deuteroporphyrin-reconstituted sperm whale metmyoglobin cyanide lead to the conclusion that the low-symmetry perturbations on the heme due to the apo-protein contacts differ for the two protein components by a 180 degrees rotation about the alpha-gamma meso axis. Hence the heme in the reconstituted myoglobin is "disordered" in solution, and the altered functional properties of the reconstituted protein cannot be simply attributed to the local effect of the heme substituent. This NMR technique has applicability for determining the relative heme orientation in related hemoproteins, and may clarify the origin of doubling of heme resonances observed in several native hemoproteins.
描述了一种用于确定卟啉在血红蛋白血红素口袋内取向的质子核磁共振方法。低自旋铁模型化合物中高精细位移的血红素甲基共振模式被证明可特征性地反映π体系上局部低对称扰动的位置。通过对氘代卟啉重构的抹香鲸高铁肌红蛋白氰化物中观察到的两组可相互转换的甲基共振进行氘代，得出的具体归属表明，由于脱辅基蛋白接触而导致的血红素上的低对称扰动，对于两种蛋白质组分而言，绕α-γ中位轴旋转180度会有所不同。因此，重构肌红蛋白中的血红素在溶液中是“无序的”，重构蛋白功能特性的改变不能简单地归因于血红素取代基的局部效应。这种核磁共振技术适用于确定相关血红蛋白中血红素的相对取向，并可能阐明在几种天然血红蛋白中观察到的血红素共振加倍的起源。
