THE JOURNAL OF BIOLOGICAL CHEMISTRY Kinetics of Oxygen and Carbon Monoxide Binding to Liver Fluke (Dicrocoelium dendriticum) Hemoglobin
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 10' and -3 X 10' M" s-', respectively, for CO and O2 and show no pH dependence. On the contrary the ligan...
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1079.1816 http://www.einstein.yu.edu/uploadedFiles/LABS/Louis_Hodgson/J%20Biol%20Chem%201985%20Di%20Iorio.pdf |
| Summary: | 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 10' and -3 X 10' M" s-', 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 relation to the fact that, in this hemoglobin, the distal histidine is replaced by a glycine. Comparative studies on the functional properties of hemoglobins, differing in their primary structure, have provided valuable information on the "mode of action" of heme proteins. Studies on hemoglobins with structural differences in the heme pocket in general and, more specifically, with the distal histidine E7 replaced by another amino acid are particularly interesting (1, 2). Heme model compounds have also been successfully used for this purpose, leading to the formulation of very interesting mechanisms for the modulation of the heme-iron reactivity (3). In the present work we report on the kinetic and some spectroscopic properties of the liver fluke Dd-Hb,' a monomeric protein with an extremely high oxygen affinity (4) and a large acid Bohr effect (5). The available structural data (6, 7),* show that, in this protein, the distal histidine is replaced by a glycine and that it represents a very old hemoglobin folding in the evolutionary scale. MATERIALS AND METHODS All operations were carried out at 4 "C unless otherwise stated. The reagents were of the highest commercially available grade and used without further purification. Sperm whale myoglobin type I1 was * This work was partially supported by the Eidgenossische Technische Hochschule Special Credits 301512DD, 04576/41-1080.5, and Schweizerischer Nationalfonds 3.199-0.82. Part of this work was presented at the Brussels Hemoglobin Symposium, Brussels,. July 23rd and 24th, 1983. The costs of publication ... |
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