Resonance Raman studies of hemoglobins M: evidence for iron-tyrosine charge-transfer interactions in the abnormal subunits of Hb M Boston and Hb M Iwate
- 1 March 1983
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 22 (5), 1305-1311
- https://doi.org/10.1021/bi00274a048
Abstract
Resonance Raman spectra were obtained for Hb M Boston [His-E7(58).alpha. .fwdarw. Tyr], Hb M Iwate [His-F8-(87).alpha. .fwdarw. Tyr] and Hb M Milwaukee [Val-E11 (67).beta. .fwdarw. Glu]. The abnormal .alpha. subunits of Hb M Boston and Hb M Iwate exhibited the porphyrin .nu.10 band at 1628 and 1627 cm-1, respectively, which indicates that the ferric .alpha. hemes are 5-coordinated in both Hb M Boston and Hb M Iwate. In addition to the porphyrin bands, 4 extra polarized lines were observed at 1607, 1506, 1278 and 603 cm-1 for the .alpha. abnormal subunit of Hb M Boston and at 1605, 1506, 1310 and 589 cm-1 for that of Hb M Iwate. By comparison with the vibrational spectra of Fe-tyrosine proteins and Fe-phenolate complexes, the 1605-1607- and 1506-cm-1 lines are assigned to the phenolate ring vibrations of the heme-coordinated tyrosine, and the 1278-cm-1 line of Hb M Boston and the 1310-cm-1 line of Hb M Iwate are assigned to the phenolate CO stretching mode. The 603-cm-1 line of Hb M Boston and the 589-cm-1 line of Hb M Iwate apparently arise from the Fe-O(tyrosine) stretching mode. These 4 Raman lines are intensity enhanced upon the excitation .apprx. 475-520 nm, probably due to the presence of a charge-transfer interaction between Fe and Tyr. The dissimilarity of the Fe-O and phenolate CO stretching frequencies between Hb M Boston and Hb M Iwate, despite the similarity of frequencies of their porphyrin and phenolate ring modes, suggests that the heme-phenolate bonding angles differ between Hb M Boston and Hb M Iwate although both adopt the 4-coordinate form with Tyr as the only axial ligand. The resonance Raman spectra of oxy- and deoxy-Hb M Milwaukee showed no anomaly and could be accounted for by those of the equimolar mixtures of aquomet- and oxy- or deoxy-Hb A.This publication has 5 references indexed in Scilit:
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