The unique heme-heme interactions of the homodimeric Scapharca inaequivalvis hemoglobin as probed in the protein reconstituted with unnatural 2,4 heme derivatives

Carlotta Zamparelli, Daniela Verzili, Alberto Boffi, Emilia Chiancone, Satoshi Takahashi, Denis L. Rousseau, Rebecca Regan, Quentin H. Gibson

Research output: Contribution to journalArticle

6 Scopus citations


In the homodimeric hemoglobin from Scapharca, HbI, functional communication between the two heme groups is based on their direct structural linkage across the subunit interface through the heme propionates. The heme- protein interactions have been altered in deutero- and meso-HbI by substituting the vinyl groups at positions 2 and 4 of protoheme with hydrogen and ethyl groups, respectively. In meso-HbI the introduction of the ethyl groups in the heme pocket induces significant alterations in the conformation of the heme peripheral substituents, including the propionates, and in the structure of bound CO, as revealed by the resonance Raman spectra. The functional counterpart of these structural changes is the loss of cooperativity in carbon monoxide binding and in the rate of oxygen dissociation. Oxygen pulse and flash photolysis experiments indicate that meso-HbI is locked in the liganded conformation. It is postulated that the ethyl groups, which occupy a larger volume than vinyl ones, impair the ligand-linked movement of the heme relative to its pocket and in turn the expression of cooperativity. In deutero-HbI structural alterations have not been monitored. Functionally, cooperativity in the CO binding kinetics is increased as if hydrogen atoms at positions 2 and 4 permitted more marked movements of the heme than in the native protein.

Original languageEnglish (US)
Pages (from-to)275-282
Number of pages8
JournalArchives of Biochemistry and Biophysics
Issue number2
Publication statusPublished - Mar 15 1997



  • cooperativity
  • dimeric hemoglobin (Scapharca)
  • unnatural heme derivatives

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

Cite this