Bismuto E, Colonna G, Savy F, Irace G
Int J Pept Protein Res. 1985 Aug;26(2):195-207. doi: 10.1111/j.1399-3011.1985.tb03197.x.
The effects of heme removal on the molecular structure of tuna and sperm whale myoglobin have been investigated by comparing the solvent accessibility to the heme pocket of the two proteins with that of the corresponding apoproteins. Although the heme microenvironment of tuna myoglobin is more polar than that of sperm whale myoglobin, the accessibility of solvent to heme is identical in the two proteins as revealed by thermal perturbation of Soret absorption. The removal of heme produces loss of helical folding and increase of solvent accessibility but the effects are rather different for the two proteins. More precisely, the loss of helical structure upon heme removal is 50% for tuna myoglobin and 15% for sperm whale myoglobin; moreover, the solvent accessibility of the heme pocket of tuna apomyoglobin is 2-3-fold greater than that of sperm whale apomyoglobin. These results have been explained in terms of the lack of helical folding in segment D, the structural organization of which may have a relevant effect in regulating the accessibility of ligands to the heme. The effects produced by charged quenchers reveal that the ligand path from the surface of the molecule to the ion atom of the heme involves a positively charged residue which may reasonably be identified as Arg-45 (sperm whale myoglobin) or Lys-41 (tuna myoglobin) on the basis of recent X-ray crystallographic information.
通过比较两种蛋白质血红素口袋的溶剂可及性与相应脱辅基蛋白的溶剂可及性，研究了去除血红素对金枪鱼和抹香鲸肌红蛋白分子结构的影响。尽管金枪鱼肌红蛋白的血红素微环境比抹香鲸肌红蛋白的更具极性，但如通过Soret吸收的热扰动所揭示的，两种蛋白质中溶剂对血红素的可及性是相同的。去除血红素会导致螺旋折叠的丧失和溶剂可及性的增加，但两种蛋白质的影响相当不同。更确切地说，去除血红素后，金枪鱼肌红蛋白的螺旋结构丧失50%，抹香鲸肌红蛋白的螺旋结构丧失15%；此外，金枪鱼脱辅基肌红蛋白血红素口袋的溶剂可及性比抹香鲸脱辅基肌红蛋白的大2至3倍。这些结果已根据D片段中缺乏螺旋折叠来解释，其结构组织可能对调节配体对血红素的可及性有相关影响。带电猝灭剂产生的影响表明，从分子表面到血红素离子原子的配体路径涉及一个带正电荷的残基，根据最近的X射线晶体学信息，该残基可能合理地被确定为抹香鲸肌红蛋白中的Arg-45或金枪鱼肌红蛋白中的Lys-41。
