Tran A T, Kalish H, Balch A L, La Mar G N
Department of Chemistry, University of California, Davis 95616, USA.
J Biol Inorg Chem. 2000 Oct;5(5):624-33. doi: 10.1007/s007750000145.
Solution 1H NMR spectroscopy was used to investigate the heme active-site structure and dynamics of rotation about the Fe-His bond of centrosymmetric etioheme-I reconstituted into sperm whale and horse myoglobin (Mb). Comparison of the NOESY cross-peak pattern and paramagnetic relaxation properties of the cyanomet complexes confirm a heme pocket that is essentially the same as Mb with either native protoheme or etioheme-I. Dipolar contacts between etioheme and the conserved heme pocket residues establish a unique seating of etioheme that conserves the orientation of the N-Fe-N vector relative to the axial His plane, with ethyl groups occupying the vinyl positions of protoheme. Saturation transfer between methyls on adjacent pyrroles in etioheme-reconstituted horse Mb in all accessible oxidation/spin states reveals rotational hopping rates that decrease dramatically with either loss of ligands or reduction of the heme, and correlate qualitatively with expectations based on the Fe-His bond strength and the rate of heme dissociation from Mb. The rate of hopping for etioheme in metMbCN, in contrast to hemes with propionates, is the same in the sperm whale and horse proteins.
利用溶液¹H核磁共振光谱研究了重组成抹香鲸和马肌红蛋白（Mb）的中心对称初卟啉-I的血红素活性位点结构以及围绕铁-组氨酸键的旋转动力学。氰化高铁配合物的NOESY交叉峰模式和顺磁弛豫特性的比较证实，血红素口袋与含有天然原卟啉或初卟啉-I的Mb基本相同。初卟啉与保守的血红素口袋残基之间的偶极接触确定了初卟啉独特的定位方式，该定位方式保持了N-Fe-N向量相对于轴向组氨酸平面的方向，乙基占据了原卟啉的乙烯基位置。在所有可及的氧化/自旋状态下，重组马Mb中初卟啉相邻吡咯上甲基之间的饱和转移揭示了旋转跳跃速率，该速率随着配体的丢失或血红素的还原而显著降低，并且与基于铁-组氨酸键强度和血红素从Mb解离速率的预期在定性上相关。与具有丙酸酯的血红素相反，高铁氰化肌红蛋白中初卟啉的跳跃速率在抹香鲸和马的蛋白质中是相同的。
