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Different structural effects of allosteric modulators on subunits of tetrameric ferrous nitrosylated human hemoglobin: an EPR spectroscopic study
Authors:Giampiero De Sanctis  Anna Maria Priori  Francesca Polizio  Paolo Ascenzi  M Coletta
Institution:(1) Department of Molecular, Cellular and Animal Biology, University of Camerino, Via F. Camerini 2, I-62032 Camerino (MC), Italy, IT;(2) INFM and Department of Biology, University of Rome Tor Vergata, Viale della Ricerca Scientifica, I-00133 Rome, Italy, IT;(3) Department of Biology, III University of Rome, Viale G. Marconi, 446, I-00146 Rome, Italy, IT;(4) Department of Experimental Medicine and Biochemical Sciences, University of Rome, Tor Vergata, Via di Tor Vergata 135, I-00133 Rome, Italy Tel.: +39-6-72596365; Fax: +39-6-72596353; e-mail: coletta@seneca.ccd.utovrm.it, IT
Abstract: The X-band EPR spectroscopic features of the ferrous nitrosylated derivative of α(Fe)2β(Co)2 and of α(Co)2β(Fe)2 metal hybrids of human hemoglobin (Hb) have been investigated at pH 7.0 and analyzed in parallel with those of the native nitrosylated tetramer (HbNO). The effect of 2,3-biphosphoglycerate (BPG), inositol hexakisphosphate (IHP) and bezafibrate (BZF) has been investigated in order to understand the perturbations induced on α and β subunits in the tetramer by the binding of allosteric effectors. A large perturbation is observed in both subunits upon BZF binding, while in the case of IHP only α-chains are affected; on the other hand, BPG leaves both chains essentially unperturbed. Thus, different binding modes of allosteric effectors to HbNO may occur, and the simultaneous addition of two effector molecules, namely BPG and BZF or IHP and BZF to HbNO, brings about different alterations of the X-band EPR spectroscopic properties. This behavior indicates that the intramolecular communication pathway(s) between the heme and the binding pockets of the heterotropic ligands (i.e., IHP and BZF, or BPG and BZF) are different, leading to distinct structural perturbations. Received: 19 September 1997 / Accepted: 16 December 1997
Keywords:  EPR spectroscopy  Hemoglobin  Metal hybrids  Nitrosylation  Perturbation  Intramolecular pathways
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