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. 2001 Jun;78(6):757.
doi: 10.1021/ed078p757.

THE OXYGEN DISSOCIATION CURVE OF HEMOGLOBIN: BRIDGING THE GAP BETWEEN BIOCHEMISTRY AND PHYSIOLOGY

Julian Gomez-Cambronero  1
Affiliations

THE OXYGEN DISSOCIATION CURVE OF HEMOGLOBIN: BRIDGING THE GAP BETWEEN BIOCHEMISTRY AND PHYSIOLOGY

Julian Gomez-Cambronero. J Chem Educ. 2001 Jun.
No abstract available

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Figures

FIGURE 1
FIGURE 1. THE CLASSICAL OXYGEN DISSOCIATION CURVE OF HEMOGLOBIN
The shape of the oxygen dissociation curve of Hb is sigmoidal, whereas that of other oxygen-carrying molecules (such as Myoglobin) is hyperbolic. Only the sigmoidal curve is characteristic of the cooperative process by which the release of one oxygen molecule alters the affinity for the remaining oxygens bound to the other proteic subunits. The 4 subunit arrangement in Hb (α1,α2,β1,β2), serves to accomplish a specific function in the organism of vertebrates, as it moves from an extreme gradient of oxygen partial pressure (or oxygen tension) from lungs to hypoxic tissues. The dashed diagonal lines in the figure indicate that oxygen molecules are bound to α/β subunits (to the sixth coordination positions of Fe2+ ions on the heme planes).
FIGURE 2
FIGURE 2. THE POSTAGE-STAMP ANALOGY
In order to release single stamps from a block of four, we have to make two cuts to release the first stamp, only one cut to release the second, and with the final cut we release the last two stamps, thus each time needing "less energy" to do the job. Similarly, oxygen remains tightly bound to hemoglobin (Hb) in the lungs but it will be progressively released as partial oxygen pressure drops in the different tissues of the body. The release of a second, and even more so the third oxygen molecule, require smaller drops in pressure as the Hb-carrying erythrocyte moves farther away to the lungs. In the analogy, Hb•4O2 exists as "four stamps bound to the 4 Hb subunits"; Hb•3O2 exists as "three stamps bound + 1 subunits free" and so on.
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