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通过共振拉曼光谱探测的五种血红蛋白M变体的血红素结构。

Heme structures of five variants of hemoglobin M probed by resonance Raman spectroscopy.

作者信息

Jin Yayoi, Nagai Masako, Nagai Yukifumi, Nagatomo Shigenori, Kitagawa Teizo

机构信息

School of Health Sciences, Kanazawa University Faculty of Medicine, Kanazawa 920-0942, Japan.

出版信息

Biochemistry. 2004 Jul 6;43(26):8517-27. doi: 10.1021/bi036170g.

Abstract

The alpha-abnormal hemoglobin (Hb) M variants show physiological properties different from the beta-abnormal Hb M variants, that is, extremely low oxygen affinity of the normal subunit and extraordinary resistance to both enzymatic and chemical reduction of the abnormal met-subunit. To get insight into the contribution of heme structures to these differences among Hb M's, we examined the 406.7-nm excited resonance Raman (RR) spectra of five Hb M's in the frequency region from 1700 to 200 cm(-1). In the high-frequency region, profound differences between met-alpha and met-beta abnormal subunits were observed for the in-plane skeletal modes (the nu(C=C), nu(37), nu(2), nu(11), and nu(38) bands), probably reflecting different distortions of heme structure caused by the out-of-plane displacement of the heme iron due to tyrosine coordination. Below 900 cm(-1), Hb M Iwate [alpha(F8)His --> Tyr] exhibited a distinct spectral pattern for nu(15), gamma(11), delta(C(beta)C(a)C(b))(2,4), and delta(C(beta)C(c)C(d))(6,7) compared to that of Hb M Boston [alpha(E7)His --> Tyr], although both heme irons are coordinated by Tyr. The beta-abnormal Hb M variants, namely, Hb M Hyde Park [beta(F8)His --> Tyr], Hb M Saskatoon [beta(E7)His --> Tyr], and Hb M Milwaukee [beta(E11)Val --> Glu], displayed RR band patterns similar to that of metHb A, but with some minor individual differences. The RR bands characteristic of the met-subunits of Hb M's totally disappeared by chemical reduction, and the ferrous heme of abnormal subunits was no longer bonded with Tyr or Glu. They were bonded to the distal (E7) or proximal (F8) His, and this was confirmed by the presence of the nu(Fe-His) mode at 215 cm(-1) in the 441.6-nm excited RR spectra. A possible involvement of heme distortion in differences of reducibility of abnormal subunits and oxygen affinity of normal subunits is discussed.

摘要

α-异常血红蛋白(Hb)M变体表现出与β-异常Hb M变体不同的生理特性,即正常亚基的氧亲和力极低,异常高铁亚基对酶促还原和化学还原均具有非凡的抗性。为了深入了解血红素结构对Hb M之间这些差异的影响,我们研究了五种Hb M在1700至200 cm⁻¹频率范围内的406.7 nm激发共振拉曼(RR)光谱。在高频区域,观察到高铁α和高铁β异常亚基在平面内骨架模式(ν(C=C)、ν(37)、ν(2)、ν(11)和ν(38)带)上存在显著差异,这可能反映了由于酪氨酸配位导致血红素铁平面外位移引起的血红素结构的不同扭曲。在900 cm⁻¹以下,与Hb M波士顿[α(E7)His→Tyr]相比,Hb M岩手[α(F8)His→Tyr]在ν(15)、γ(11)、δ(CβCaC(b))(2,4)和δ(CβCcCd)(6,7)处表现出独特的光谱模式,尽管两个血红素铁均由酪氨酸配位。β-异常Hb M变体,即Hb M海德公园[β(F8)His→Tyr]、Hb M萨斯卡通[β(E7)His→Tyr]和Hb M密尔沃基[β(E11)Val→Glu],显示出与高铁血红蛋白A相似的RR带模式,但存在一些微小的个体差异。Hb M的高铁亚基特征性的RR带通过化学还原完全消失,异常亚基的亚铁血红素不再与酪氨酸或谷氨酸结合。它们与远端(E7)或近端(F8)组氨酸结合,这在441.6 nm激发的RR光谱中215 cm⁻¹处存在ν(Fe-His)模式得到证实。本文讨论了血红素扭曲可能与异常亚基还原性差异和正常亚基氧亲和力差异有关。

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