EPR OF METHEMOGLOBIN FORMATION IN RED CELLS W/ UNSTABLE HEMOGLOBIN

从衣原体真配子体的叶绿体中提取的血红蛋白， 克隆并在E.杆菌 这种血红蛋白类似于几种 在B10位置具有tyr残基并且在E7位置具有glut， 据信这两者都参与了与结合O2的H键合 这导致了极慢的解离速率。 另一方面，在一项研究中， 衣原体血红蛋白是不寻常的，因为铁蛋白具有一个 高自旋到低自旋（六配位）跃迁pK为8.5，而 铁蛋白具有高自旋到低自旋（六配位） 转变pK为6.4。 这表明，低分子量的远端配体 亚铁和铁蛋白的自旋形式可能不同。 铁蛋白表现出单一的低自旋形式，g值为 2.52，2.31，1.86，因此各向异性类似于肌红蛋白 氢氧化 然而，17 O EPR和18 O共振拉曼研究未能 提供了氢氧化物配体的直接证据 光谱研究 B10 Tyr、E7 Gln和E10 Lys残基的远端突变体 至今未能鉴定出可能的氨基酸配体。 进一步 正在进行研究以鉴定远端配体， 了解不寻常的低自旋EPR谱。

A Hb from the chloroplast of Chlamydomonas eugametos has been cloned andexpressed in E. coli. This Hb resembles several invetebrate in having a tyr residue in the B10 and a glut in the E7 positions, both of which are believed to participate in H-bonding to bound O2 that results in extremely slow off-rates. On the other hand, Chlamydomonas Hb is unusual in that the ferrous protein has a high-spin to low spin (six-coordinate) transition pK of 8.5, whereas the ferric protein has a high-spin to low spin (six-coordinate) transition pK of 6.4. This suggests that the distal ligand of the low spin forms of the ferrous and the ferric proteins may be different. The ferric protein exhibits a single low spin form with g values of 2.52, 2.31, 1.86, and thus an anisotropy similar to that of myoglobin hydroxide. However, 17O EPR and 18O resonance Raman studies failed to provide direct evidence for a hydroxide ligand. Spectroscopic studies on the distal mutants of the B10 Tyr, E7 Gln, and the E10 Lys residues have so far failed to identify a possible amino acid ligand. Further studies are being conducted to identify the distal ligand and to understand the unusual low spin EPR spectrum.