Heme regulatory motifs in heme oxygenase-2 form a thiol/disulfide redox switch that responds to the cellular redox state

J Biol Chem. 2009 Jul 31;284(31):20556-61. doi: 10.1074/jbc.M109.015651. Epub 2009 May 27.


Heme oxygenase (HO) catalyzes the rate-limiting step in heme catabolism to generate CO, biliverdin, and free iron. Two isoforms of HO have been identified in mammals: inducible HO-1 and constitutively expressed HO-2. HO-1 and HO-2 share similar physical and kinetic properties but have different physiological roles and tissue distributions. Unlike HO-1, which lacks cysteine residues, HO-2 contains three Cys-Pro signatures, known as heme regulatory motifs (HRMs), which are known to control processes related to iron and oxidative metabolism in organisms from bacteria to humans. In HO-2, the C-terminal HRMs constitute a thiol/disulfide redox switch that regulates affinity of the enzyme for heme (Yi, L., and Ragsdale, S. W. (2007) J. Biol. Chem. 282, 20156-21067). Here, we demonstrate that the thiol/disulfide switch in human HO-2 is physiologically relevant. Its redox potential was measured to be -200 mV, which is near the ambient intracellular redox potential. We expressed HO-2 in bacterial and human cells and measured the redox state of the C-terminal HRMs in growing cells by thiol-trapping experiments using the isotope-coded affinity tag technique. Under normal growth conditions, the HRMs are 60-70% reduced, whereas oxidative stress conditions convert most (86-89%) of the HRMs to the disulfide state. Treatment with reductants converts the HRMs largely (81-87%) to the reduced dithiol state. Thus, the thiol/disulfide switch in HO-2 responds to cellular oxidative stress and reductive conditions, representing a paradigm for how HRMs can integrate heme homeostasis with CO signaling and redox regulation of cellular metabolism.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Motifs
  • Cell Line
  • Disulfides / metabolism*
  • Escherichia coli
  • Heme / metabolism*
  • Heme Oxygenase (Decyclizing) / chemistry*
  • Heme Oxygenase (Decyclizing) / isolation & purification
  • Heme Oxygenase (Decyclizing) / metabolism*
  • Humans
  • Mass Spectrometry
  • Oxidation-Reduction
  • Sulfhydryl Compounds / metabolism*


  • Disulfides
  • Sulfhydryl Compounds
  • Heme
  • Heme Oxygenase (Decyclizing)
  • heme oxygenase-2