Kinetics of oxygen and carbon monoxide binding to liver fluke (Dicrocoelium dendriticum) hemoglobin. An extreme case?

The kinetics of oxygen and carbon monoxide binding to the monomeric liver fluke (Dicrocoelium dendriticum) hemoglobin have been studied. The ligand association rates are ~1 x 10⁸ and ~3 x 10⁸ M^-1 s^-1, respectively, for CO and O₂ and show no pH dependence. On the contrary the ligand dissociation rates decrease by lowering the pH below 7, the pK of the transition being around 5.5. These findings, together with spectroscopic properties of the protein, are discussed in ralation to the fact that, in this hemoglobin, the distal histidine is replaced by a glycine.