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 language | English |
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Pages (from-to) | 239-244 |
Number of pages | 6 |
Journal | Biochemical and Biophysical Research Communications |
Volume | 428 |
Issue number | 2 |
DOIs | |
Publication status | Published - 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