Resonance Raman spectra of methemoglobin derivatives. Selective enhancement of axial ligand vibrations and lack of an effect of inositol hexaphosphate
Resonance Raman spectra have been obtained for the OH/sup -/, N/sub 3//sup -/, and F/sup -/ derivatives of methemoglobin by excitation in the 550 to 650-nm region. A selective enhancement with excitation in the charge-transfer bands is observed for peaks at 413 and 497 cm/sup -1/ and a doublet at 471 and 443 cm/sup -1/ in the N/sub 3//sup -/, OH/sup -/, and F/sup -/ complexes, respectively. These peaks are assigned to Fe-axial ligand stretches on the basis of: (1) a 20-cm/sup -1/ shift of the 497-cm/sup -1/ peak of the hydroxide complex to lower energy on isotopic substitution of /sup 18/OH/sup -/ for /sup 16/OH/sup -/; (2) the proximity of the 413-cm/sup -1/ Raman peak to the 421-cm/sup -1/ IR peak previously assigned to the Fe--N/sub 3//sup -/ stretch in a model heme-azide complex (Ogoshi, H., Watenabe, E., Yoshida, Z., Kincaid, J., and Nakamoto, K. (1973), J. Am. Chem. Soc. 95, 2845); (3) the selective appearance of the 471- and 443-cm/sup -1/ peaks in the Raman spectra of the F/sup -/ complex. The doublet observed at 471 and 443 cm/sup -1/ in the F/sup -/ derivative may reflect a heterogeneity in the heme cavity due to hydrogen bonding of H/sub 2/O to the F/sup -/ ligand in both the ..cap alpha.. and ..beta.. subunits, as has been previously suggested based on x-ray diffraction results. It is suggested that the frequency of the Fe--F/sup -/ vibration reflects the out-of-plane distortion of the Fe from the heme plane. The lack of a shift in the frequency of the Fe--F/sup -/ vibration suggests that there is little or no movement of the iron with respect to the heme plane upon the addition of inositol hexaphosphate, which is thought to alter the allosteric equilibrium between the R and T forms of methemoglobin. This result is consistent with a recent x-ray crystallographic study of an IHP complex of MetHb--F/sup -/. Excitation profile measurements suggest that the charge-transfer band in methemoglobin OH/sup -/ like that in methemoglobin N/sub 3//sup -/ is z polarized, while in methemoglobin F/sup -/ the charge transfer transition is mixed with a ..pi.. to ..pi..* transition.
- Research Organization:
- Univ. of California, Berkeley, CA (United States)
- OSTI ID:
- 7277205
- Journal Information:
- Biochemistry; (United States), Vol. 16:26
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AZIDO COMPOUNDS
CHARGE TRANSPORT
RAMAN SPECTRA
HYDROXIDES
IRON
LIGANDS
VIBRATIONAL STATES
METHEMOGLOBIN
STRUCTURAL CHEMICAL ANALYSIS
ORGANIC FLUORINE COMPOUNDS
INOSITOLS
ORGANIC PHOSPHORUS COMPOUNDS
CARBOHYDRATES
CARBOXYLIC ACIDS
ELEMENTS
ENERGY LEVELS
EXCITED STATES
GLOBIN
HEMOGLOBIN
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
METALS
MONOSACCHARIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PIGMENTS
PORPHYRINS
PROTEINS
SACCHARIDES
SPECTRA
TRANSITION ELEMENTS
550200* - Biochemistry
400104 - Spectral Procedures- (-1987)