Heterotropic effectors exert more significant strain on monoligated than on unligated hemoglobin.
The effect of allosteric effectors, such as inositol hexakisphosphate and/or bezafibrate, has been investigated on the unliganded human adult hemoglobin both spectroscopically (employing electronic absorption, circular dichroism, resonance Raman, and x-ray absorption near-edge spectroscopies) and functionally (following the kinetics of the first CO binding step up to a final 4% ligand saturation degree). All data indicate that the unliganded T-state is not perturbed by the interaction with either one or both effectors, suggesting that their functional influence is only exerted when a ligand molecule is bound to the heme. This is confirmed by the observation that CO dissociation from partially liganded hemoglobin ( </= 0.04) is strongly altered by the presence of either effector, and the effect is enhanced whenever the two effectors are simultaneously present. Altogether, these data are a direct demonstration of the occurrence of a strain induced by the presence of a ligand molecule bound to the heme, and for the first time there is a clear indication that the expression of the functional heterotropic effect by these non-heme ligands requires this strain, which is not present in the unliganded molecule.
Department of Experimental Medicine and Biochemical Sciences, University of Roma Tor Vergata, I-00133 Roma, Italy. coletta@seneca.uniroma2.it
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Angeletti
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Ascone
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Boumis
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Castellano
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Dell'Ariccia
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Della Longa
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De Sanctis
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Priori
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Santucci
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Amiconi
D000328:Adult; D000494:Allosteric Regulation; D001629:Bezafibrate; D055592:Biophysical Phenomena; D001703:Biophysics; D002248:Carbon Monoxide / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008024:Ligands; D010833:Phytic Acid; D011487:Protein Conformation; D013057:Spectrum Analysis
D006454:Hemoglobins; D008024:Ligands; D010833:Phytic Acid; D002248:Carbon Monoxide; D001629:Bezafibrate