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.
|Data di pubblicazione:||2004|
|Titolo:||Nitrosylation of rabbit ferrous heme-hemopexin|
|Digital Object Identifier (DOI):||10.1007/s00775-004-0598-0|
|Codice identificativo ISI:||WOS:000224751400002|
|Codice identificativo Scopus:||2-s2.0-8644232439|
|Parole Chiave:||Ferrous nitrosylated heme-hemopexin; Heme-iron geometry; NO binding properties; Rabbit hemopexin; Spectroscopic properties|
|Appare nelle tipologie:||Articolo su Rivista|