Metastable intermediates in myoglobin at low pH

Sanghwa Han, Denis L. Rousseau, Giorgio Giacometti, Maurizio Brunori

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

Resonance Raman and optical absorption spectra of ligand-free (deoxy) myoglobin and CO-bound myoglobin (MbCO) at pH 2,6 have been measured by using continuous-flow/rapid-mixing techniques. The spectra of deoxy myoglobin at low pH within 6 ms of the pH drop demonstrate that the iron-histidine bond has been ruptured but that the heme is still five-coordinate. Comparison with data from model complexes indicates that a weak-field ligand, such as a water molecule, is coordinated at the fifth position. The Raman spectrum of MbCO at low pH has an Fe - CO stretching mode that is characteristic of a six-coordinate heme with an unhindered Fe - CO moiety. Immediately following the pH drop in this case, there is no indication that the iron-proximal histidine bond is broken. Three different structural changes are detected at low pH: (i) the iron-proximal histidine (F8) bond in ligand-free myoglobin is broken and replaced by a weak-field ligand, (ii) the distal pocket in MbCO is opened, and (iii) protein constraints on the heme group in MbCO are relaxed. Previous conclusions that the kinetics of CO-binding in hemoproteins at low pH is modified by rupturing the iron-proximal histidine bond are supported by these new results which, however, demand a more complete reevaluation of the phenomenon.

Original languageEnglish (US)
Pages (from-to)205-209
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume87
Issue number1
StatePublished - 1990
Externally publishedYes

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Myoglobin
Carbon Monoxide
Histidine
Iron
Heme
Ligands
Water

ASJC Scopus subject areas

  • Genetics
  • General

Cite this

Metastable intermediates in myoglobin at low pH. / Han, Sanghwa; Rousseau, Denis L.; Giacometti, Giorgio; Brunori, Maurizio.

In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 87, No. 1, 1990, p. 205-209.

Research output: Contribution to journalArticle

Han, Sanghwa ; Rousseau, Denis L. ; Giacometti, Giorgio ; Brunori, Maurizio. / Metastable intermediates in myoglobin at low pH. In: Proceedings of the National Academy of Sciences of the United States of America. 1990 ; Vol. 87, No. 1. pp. 205-209.
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