BioMetals

, Volume 21, Issue 3, pp 239–248

An investigation of hemopexin redox properties by spectroelectrochemistry: biological relevance for heme uptake

Authors

  • Meghan M. Flaherty
    • Department of ChemistryDuke University
  • Kimberley R. Rish
    • Division of Molecular Biology and Biochemistry, School of Biological SciencesUniversity of Missouri – K.C.
  • Ann Smith
    • Division of Molecular Biology and Biochemistry, School of Biological SciencesUniversity of Missouri – K.C.
    • Department of ChemistryDuke University
Article

DOI: 10.1007/s10534-007-9112-9

Cite this article as:
Flaherty, M.M., Rish, K.R., Smith, A. et al. Biometals (2008) 21: 239. doi:10.1007/s10534-007-9112-9

Abstract

Hemopexin (HPX) has two principal roles: it sequesters free heme in vivo for the purpose of preventing the toxic effects of this moiety, which is largely due to heme’s ability to catalyze free radical formation, and it transports heme intracellularly thus limiting its availability as an iron source for pathogens. Spectroelectrochemistry was used to determine the redox potential for heme and meso-heme (mH) when bound by HPX. At pH 7.2, the heme-HPX assembly exhibits E1/2 values in the range 45–90 mV and the mH-HPX assembly in the range 5–55 mV, depending on environmental electrolyte identity. The E1/2 value exhibits a 100 mV positive shift with a change in pH from 7.2 to 5.5 for mH-HPX, suggesting a single proton dependent equilibrium. The E1/2 values for heme-HPX are more positive in the presence of NaCl than KCl indicating that Na+, as well as low pH (5.5) stabilizes ferro-heme-HPX. Furthermore, comparing KCl with K2HPO4, the chloride salt containing system has a lower potential, indicating that heme-HPX is easier to oxidize. These physical properties related to ferri-/ferro-heme reduction are both structurally and biologically relevant for heme release from HPX for transport and regulation of heme oxygenase expression. Consistent with this, when the acidification of endosomes is prevented by bafilomycin then heme oxygenase-1 induction by heme-HPX no longer occurs.

Keywords

HemeMeso-hemeHemopexinIronHemophoreHeme transportRedoxEndocytosis

Abbreviations

DMEM

Dulbecco’s Minimal Essential Medium

HEPES

4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid

H

Heme, protoporphyrin-IX

HO-1

Heme oxygenase-1

HPX

Hemopexin

mH

Meso-heme

NHE

Normal hydrogen electrode

OTTLE

Optically transparent thin-layer electrode

SDS

Sodium dodecyl sulfate

Copyright information

© Springer Science+Business Media BV 2007