Nitrosylation of rabbit ferrous heme-hemopexin |
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Authors: | Mauro?Fasano Alessio?Bocedi Marco?Mattu Massimo?Coletta Email author" target="_blank">Paolo?AscenziEmail author |
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Institution: | (1) Department of Structural and Functional Biology, University of Insubria, Via Alberto da Giussano 12, 21052 Busto Arsizio (VA), Italy;(2) Department of Biology and Interdepartmental Laboratory for Electron Microscopy, University Roma Tre, Viale Guglielmo Marconi 446, 00146 Rome, Italy;(3) Department of Chemistry, Chemical Engineering and Materials, University of LAquila, Via Vetoio, Coppito, 67100 LAquila, Italy;(4) INMI, National Institute for Infectious Diseases IRCCS Lazzaro Spallanzani, Via Portuense 292, 00149 Rome, Italy;(5) IRBM, Research Institute for Molecular Biology P. Angeletti, Via Pontina km 30.600, 00040 Pomezia (RM), Italy;(6) Department of Experimental Medicine and Biochemical Sciences, University of Rome Tor Vergata, Via Montpellier 1, 00133 Rome, Italy |
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Abstract: | Hemopexin (HPX) serves as a trap for toxic plasma heme, ensuring its complete clearance by transportation to the liver. Moreover, HPX-heme has been postulated to play a key role in the homeostasis of nitric oxide (NO). Here, the thermodynamics for NO binding to rabbit ferrous HPX-heme as well as the EPR and optical absorption spectroscopic properties of rabbit ferrous nitrosylated HPX-heme (HPX-heme-NO) are reported. The value of the dissociation equilibrium constant for NO binding to rabbit ferrous HPX-heme (i.e., H) is (1.4±0.2)×10–7 M, at pH 7.0 and 10.0 °C; the value of H is unaffected by sodium chloride. At pH 7.0, rabbit ferrous HPX-heme-NO is a six-coordinate heme-iron species, characterized by an X-band EPR spectrum with an axial geometry and by =146 mM–1 cm–1 at 419 nm. At pH 4.0, rabbit ferrous HPX-heme-NO is a five-coordinate heme-iron species, characterized by an X-band EPR spectrum with three-line splitting centered at 334 mT and by =74 mM–1 cm–1 at 387 nm. The pKa value of the reversible pH-induced six- to five-coordinate spectroscopic transition is 4.8±0.1 in the absence of sodium chloride and 4.3±0.1 in the presence of 1.5×10–1 M sodium chloride. This result is in agreement with the effect of sodium chloride on rabbit HPX-heme stability. The present data have been analyzed in parallel with those of a related heme model compound and heme-protein systems. |
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Keywords: | Ferrous nitrosylated heme-hemopexin Heme-iron geometry NO binding properties Rabbit hemopexin Spectroscopic properties |
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