Cyanide binding to human plasma heme-hemopexin: A comparative study

Paolo Ascenzi, Loris Leboffe, Fabio Polticelli

Research output: Contribution to journalArticlepeer-review

Abstract

Hemopexin (HPX) displays a pivotal role in heme scavenging and delivery to the liver. In turn, heme-Fe-hemopexin (HPX-heme-Fe) displays heme-based spectroscopic and reactivity properties. Here, kinetics and thermodynamics of cyanide binding to ferric and ferrous hexa-coordinate human plasma HPX-heme-Fe (HHPX-heme-Fe(III) and HHPX-heme-Fe(II), respectively), and for the dithionite-mediated reduction of the HHPX-heme-Fe(III)-cyanide complex, at pH 7.4 and 20.0°C, are reported. Values of thermodynamic and kinetic parameters for cyanide binding to HHPX-heme-Fe(III) and HHPX-heme-Fe(II) are K=(4.1±0.4)×10-6M, kon=(6.9±0.5)×101M-1s-1, and koff=2.8×10-4s-1; and H=(6±1)×10-1M, hon=1.2×10-1M-1s-1, and hoff=(7.1±0.8)×10-2s-1, respectively. The value of the rate constant for the dithionite-mediated reduction of the HHPX-heme-Fe(III)-cyanide complex is l=8.9±0.8M-1/2s-1. HHPX-heme-Fe reactivity is modulated by proton acceptor/donor amino acid residue(s) (e.g., His236) assisting the deprotonation and protonation of the incoming and outgoing ligand, respectively.

Original languageEnglish
Pages (from-to)239-244
Number of pages6
JournalBiochemical and Biophysical Research Communications
Volume428
Issue number2
DOIs
Publication statusPublished - Nov 16 2012

Keywords

  • Ce-trHbN
  • Cj-trHbP
  • Cyanide binding
  • Hb
  • HDL
  • HHPX
  • HHPX-heme-Fe
  • HHPX-heme-Fe(II)
  • HHPX-heme-Fe(III)
  • HPX
  • HPX-heme-Fe
  • Human heme-hemopexin
  • Kinetics
  • LDL
  • LegHb
  • Mb
  • Molecular modeling
  • Mt-trHbN
  • Mt-trHbO
  • Ngb
  • SA
  • Thermodynamics
  • TrHb

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Cell Biology
  • Molecular Biology

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