Resonance Raman spectroscopic studies of axial ligation in oxyhemoglobin, oxymyoglobin, and nitrosylmyoglobin

Marc Walters, T. G. Spiro

Research output: Contribution to journalArticle

Abstract

Raman intensity measurements for the Fe-O2 stretching band of HbO2 (Hb = hemoglobin) have been used to construct an excitation profile, which shows that resonance enhancement occurs mainly via the B and Q transition; no contribution is detectable from an out-of-plane charge-transfer transition. Direct coupling of νFe-o2 to the porphyrin π-π* transitions is explained on the basis of competition between the π* orbitals of porphyrin and O2 for Fe dπ electrons. The RR spectrum of MbNO (Mb = myoglobin) at pH 8.4 is due solely to six-coordinate heme-NO, but lowering the pH to 5.8 converts the RR spectrum to one characteristic of five-coordinate heme-NO, consistent with Fe-ImH (ImH = imidazole) dissociation via protonation. The Fe-NO stretching frequencies are at 553 and 596 cm-1 for the high- and low-pH forms, as expected, but the low-pH form shows an additional 15NO-sensitive band, at 573 cm-1, which is assigned to Fe-N-O bending in the five-coordinate complex. The RR spectrum of MbO2 shows a shoulder at ∼270 cm-1, which shifts down by ∼3 cm-1 upon 18O2 substitution, and is suggested to contain the Fe-ImH stretching mode. The weakness of νFe-ImH, relative to νFe-o2, is attributable to the lack of ImH involvement in the heme π bonding.

Original languageEnglish (US)
Pages (from-to)6989-6995
Number of pages7
JournalBiochemistry
Volume21
Issue number26
StatePublished - 1982

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Oxyhemoglobins
Heme
Stretching
Ligation
Porphyrins
Myoglobin
Protonation
Charge transfer
Hemoglobins
Substitution reactions
Electrons
oxymyoglobin
myoglobin nitroxide

ASJC Scopus subject areas

  • Biochemistry

Cite this

Resonance Raman spectroscopic studies of axial ligation in oxyhemoglobin, oxymyoglobin, and nitrosylmyoglobin. / Walters, Marc; Spiro, T. G.

In: Biochemistry, Vol. 21, No. 26, 1982, p. 6989-6995.

Research output: Contribution to journalArticle

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