title: Resonance Raman evidence for cleavage of the Fe-N epsilon(His-F8) bond in the alpha subunit of the T-structure nitrosylhemoglobin.
abstract: Resonance Raman spectra are observed for hybrid nitrosylhemoglobins (NO-Hb) reconstituted from normal and meso-deuterated hemes and also for penta- and hexa-coordinated NO-heme complexes. Upon meso deuteration of both hemes of the alpha and beta subunits [alpha(D)2NO beta(D)2NO], the Raman lines of stripped NO-Hb at 1636 (dp), 1584 (ap), and 1502 (p) cm-1 are shifted by -10, -20, and -7 cm-1, respectively, and those at 1306 (ap) and 1228 (dp) cm-1 disappear. The spectral changes caused by meso deuteration are in good agreement with those observed previously for (octaethyl-porphyrinato)nickel(II), for which the vibrational assignments of resonance Raman lines have been established. Accordingly, the 1636-, 1584-, 1502-, 1306-, and 1228-cm-1 lines of NO-Hb are assigned to nu 10, nu 19, nu 3, nu 21, and nu 13, respectively. Upon conversion from the R to the T structure, both nu 19 and nu 3 are shifted to higher frequencies by 4 cm-1 and nu 10 is split into two lines at 1645 and 1637 cm-1. The 1645-cm-1 line remains unshifted after meso deuteration of the beta heme [alpha(H)2NO beta-(D)2NO], and, conversely, the 1637-cm-1 line remains unshifted after meso deuteration of the alpha heme [alpha(D)2NO beta(H)2NO]. On the basis of the Raman spectra of the model NO-heme complexes, the 1645- and 1637-cm-1 lines are assigned to the penta- and hexacoordinated NO-heme complexes. Consequently, we conclude that the Fe-N epsilon(His-F8) of the alpha subunit within NO-Hb is disrupted in the T structure, while the NO-heme of the beta subunit adopts the hexacoordinated structures, in good agreement with our previous electron paramagnetic resonance work. The Raman spectra of the isolated alpha NO and beta NO chains are appreciably different. The Raman lines of the isolated alpha NO chain at 1606 (p), 1587 (ap), and 1504 (p) cm-1 are shifted by -6, +5, and +4 cm-1 when it is incorporated into the T-structure tetramer. In contrast, all the Raman lines of the isolated beta NO chain are not shifted in the T-structure tetramer.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D006454:Hemoglobins; D006801:Humans; D009603:Nitroso Compounds; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman
chemical_list: D006454:Hemoglobins; D009603:Nitroso Compounds; C008657:nitrosyl hemoglobin