Smulevich G, Mantini A R, Paoli M, Coletta M, Geraci G
Department of Chemistry, University of Firenze, Italy.
Biochemistry. 1995 Jun 6;34(22):7507-16. doi: 10.1021/bi00022a026.
A spectroscopic investigation by resonance Raman has been carried out at pH 7.0 in 0.1 M phosphate buffer on the cooperative homodimeric myoglobin from Nassa mutabilis. The study has been performed on the unligated ferrous form, as well as on the ligated species MbO2 and MbC, and on the ferric form met-Mb. Two v(C = C) vinyl stretching modes have been observed in all the investigated forms, reflecting different degrees of vinyl conjugation with the porphyrin ring, as a consequence of a strongly asymmetric environment for the two side groups of the heme. Furthermore, the ferric form displays a hexacoordinate low-spin heme, which suggests the presence of an endogenous ligand bound to the Fe atom. The frequency of the v(Fe-Im) stretching mode of Mb from Nassa mutabilis shifts down by 4 cm-1 as compared with that of horse heart myoglobin, reflecting a protein-induced proximal strain as a result of heme-heme interaction due to the close proximity of the two hemes in the dimer. The lower frequency of the v(Fe-Im) stretching mode agrees well with the lower affinity for oxygen binding found for Nassa mutabilis Mb and with the slight heme core expansion with respect to horse heart Mb, suggesting a critical role for the Fe-His bond on the heme's function and structure.
在pH 7.0的0.1 M磷酸盐缓冲液中，利用共振拉曼光谱对来自多变织纹螺的协同同二聚体肌红蛋白进行了研究。该研究针对未结合配体的亚铁形式、结合配体的物种MbO2和MbC以及高铁形式的高铁肌红蛋白进行。在所有研究形式中均观察到两种v(C = C)乙烯基伸缩模式，这反映了由于血红素两个侧基的环境强烈不对称，乙烯基与卟啉环的共轭程度不同。此外，高铁形式显示出六配位低自旋血红素，这表明存在与铁原子结合的内源性配体。与马心肌红蛋白相比，多变织纹螺肌红蛋白的v(Fe-Im)伸缩模式频率下降了4 cm-1，这反映了由于二聚体中两个血红素靠得很近，血红素-血红素相互作用导致的蛋白质诱导的近端应变。v(Fe-Im)伸缩模式的较低频率与多变织纹螺肌红蛋白对氧结合的较低亲和力以及相对于马心肌红蛋白血红素核心的轻微扩张非常吻合，这表明铁-组氨酸键对血红素的功能和结构起着关键作用。
