Anion- and pH-linked effects on the heme-iron geometry in ferrous nitrosylated monomeric myoglobins |
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Authors: | Francesca Polizio Giampiero De Sanctis Paolo Ascenzi M. Coletta |
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Affiliation: | (1) INFM Department of Biology, University of Rome "Tor Vergata", I-00173 Rome, Italy, IT;(2) Department of Molecular, Cellular and Animal Biology, University of Camerino, I-62032 Camerino (MC), Italy, IT;(3) Department of Biology, Third University of Rome, I-00154 Rome, Italy, IT;(4) Department of Experimental Medicine and Biochemical Sciences, University of Rome Tor Vergata, I-00133 Rome, Italy e-mail: coletta@seneca.uniroma2.it, Tel.: +39-6-72596365, Fax: +39-6-72596353, IT |
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Abstract: | The cooperative effect of anions and proton concentration on the EPR spectroscopic properties of the ferrous nitrosylated derivative of monomeric Mb from loggerhead sea turtle (Caretta caretta), sperm whale (Physeter catodon), and horse (Caballus caballus) has been investigated between pH 4.5 and 9.0, at 100 K. In the absence of anions, an EPR spectrum characteristic of the hexa-coordinated species of ferrous nitrosylated Mb with an axial geometry is observed, which is unaffected by pH. On the other hand, a transition toward a species characterized by an EPR spectrum corresponding to a hexa-coordinated rhombic geometry takes place in the presence of phosphate, acetate, citrate, sulfate, and chloride. Only the hexa-coordinated form characterized by the rhombic EPR spectrum appears then to undergo a pH-dependent transition toward the penta-coordinated species. Present results show clear-cut evidence for the spectroscopic coupling of proton and anion binding sites with the Mb reactive center, indicating that an allosteric mechanism might modulate the proximal HisF8-heme-NO geometry in monomeric hemoproteins. Received: 15 December 1997 / Accepted: 15 June 1998 |
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Keywords: | Ferrous nitrosylated myoglobin Heme-iron geometry EPR spectroscopy Inorganic phosphate (effect of) Anion/proton synergism |
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