Heme oxygenases from Arabidopsis thaliana reveal different mechanisms of carbon monoxide binding.
Heme oxygenases (HO) are widely distributed enzymes involved in the degradation of heme to biliverdin, carbon monoxide and Fe(2+). The model plant Arabidopsis thaliana possesses three functional HOs (HY1, HO3 and HO4) which are thus far biochemically indistinguishable. Here, we investigate binding of the reaction product and putative inhibitor CO to these three HOs with various spectroscopic techniques: Nanosecond time-resolved absorption, millisecond time-resolved multi-wavelength absorption and Fourier-transform-infrared difference spectroscopy. Kinetics of CO rebinding were found to differ substantially among the HOs. At low CO concentrations a novel intermediate was identified for HO3 and HO4, substantially slowing down rebinding. All HOs show relatively slow geminate rebinding of CO indicating the existence of an additional transient binding niche for CO. The positions found for the IR absorptions of ν(CO) and ν(FeC) suggest a nonpolar distal binding site for all three HOs. The frequency of the ν(FeC) vibration was calculated by a combination band on which we report here for the first time. Another band in the FTIR difference spectrum could be assigned to a histidine residue, probably the proximal ligand of the heme-iron. The observed different rebinding kinetics among the HOs could indicate adaptation of the HOs to different environments.
Physiology of Microorganisms, Ruhr-University Bochum, Bochum, Germany.
Björn
B
Gisk
Bastian
B
Molitor
Nicole
N
Frankenberg-Dinkel
Carsten
C
Kötting
D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002248:Carbon Monoxide / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D007700:Kinetics; D011485:Protein Binding; D017550:Spectroscopy, Fourier Transform Infrared
D029681:Arabidopsis Proteins; D006418:Heme; D002248:Carbon Monoxide; D006419:Heme Oxygenase (Decyclizing)