Blood is an amazing and vitally important part of the body, because it contains many finely-tuned chemical systems that allow it to maintain the chemical environment needed for the body's metabolism. One of the most important functions of blood is delivering O2 to all parts of the body by the hemoglobin protein. O2 is carried in the hemoglobin protein by the heme group. The heme group (a component of the hemoglobin protein) is a metal complex, with iron as the central metal atom, that can bind or release molecular oxygen. Both the hemoglobin protein and the heme group undergo conformational changes upon oxygenation and deoxygenation. When one heme group becomes oxygenated, the shape of hemoglobin changes in such a way as to make it easier for the other three heme groups in the protein to become oxygenated, as well. This feature helps the protein to pick up oxygen more efficiently as the blood travels through the lungs. Hemoglobin also enables the body to eliminate CO2, which is generated as a waste product, via gas exchange in the blood (CO2 exchanged for O2 in the lungs, and O2 exchanged for CO2 in the muscles). The species generated as waste by the oxygen-consuming cells actually help to promote the release of O2 from hemoglobin when it is most needed by the cells. Hence, hemoglobin is a beautiful example of the finely tuned chemical systems that enable the blood to distribute necessary molecules to cells throughout the body, and remove waste products from those cells.
To view the molecules interactively, please use Jmol. To download the pdb files for viewing and rotating the molecules, please click on the appropriate name below or on the "interactive" button below each molecular-model figure in the text.
Guex, N. and Peitsch, M.C. Electrophoresis, 1997, 18, 2714-2723. (SwissPDB Viewer) URL: http://www.expasy.ch/spdbv/mainpage.htm.
Ji, X. et al. "Positive and negative cooperativities at subsequent steps of oxygenation regulate the allosteric behavior of multistate sebacylhemoglobin," (1996) Biochemistry, 35, 3418. Hemoglobin PDB coordinates, Brookhaven Protein Data Bank.
Kavanaugh, J.S. et al. "High-resolution x-ray study of deoxyhemoglobin Rothschild 37beta trp->arg: a mutation that creates an intersubunit chloride-binding site," (1992) Biochemistry, 31, 4111. Deoxyhemoglobin PDB coordinates, Brookhaven Protein Data Bank.
Kilmartin, J.V. "Interaction of haemoglobin with protons, CO2, and 2,3-diphosphoglycerate," (1976) Br. Med. Bull., 32, 209.
Persistence of Vision Ray Tracer (POV-Ray). URL: http://www.povray.org.
Royer Jr., W.E. "High-resolution crystallographic analysis of co-operative dimeric hemoglobin," J. Mol. Biol., 235, 657. Oxyhemoglobin PDB coordinates, Brookhaven Protein Data Bank.
Stryer, L. Biochemistry, 4th ed. W.H. Freeman and Co., New York, 1995, p. 154-168.
The authors thank Greg Noelken for creating the jmol script files. They also wish to thank Dewey Holten, Michelle Gilbertson, Jody Proctor and Carolyn Herman for many helpful suggestions in the writing of this tutorial.
The development of this tutorial was supported by a grant from the Howard Hughes Medical Institute, through the Undergraduate Biological Sciences Education program, Grant HHMI# 71199-502008 to Washington University.
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