Oxygen dissociation curve of hemoglobin

Hyperbolic shape of the enzyme kinetics curve Most enzymes show Michaelis-Menten kinetics (see p. 58), in which the plot of initial reaction velocity, v0, against substrate concentration [S], is hyperbolic (similar in shape to that of the oxygen-dissociation curve of myoglobin, see p. 29). In contrast, allosteric enzymes frequently show a sigmoidal curve (see p. 62) that is similar in shape to the oxygen-dissociation curve of hemoglobin (see p. 29). 

Early this century, A.V. Hill derived a useful equation that describes the oxygen dissociation curve of hemoglobin fairly accurately. It is... 

Ascorbic acid appears to be toxic to certain tumor tissues however, it may increase the biological effectiveness of red blood cells by increasing the level of 2,3-diphosphoglycerate (30,31), 2,3-Diphosphoglycerate is essential to maintaining the normal oxygen dissociation curve of hemoglobin. This increase has been shown in vitro (30) and in vivo, in human subjects (31). 

Adair, G.S. 1925. The hemoglobin system. VI. The oxygen dissociation curve of hemoglobin. J. Biol. Chem. 63 529-45. 

G. S. Adair, The Hemoglobin System. VI. The Oxygen Dissociation Curve of Hemoglobin. J. Biol Chem., 63,529-545,1925. 

I. A 10-month-old child is being evaluated for the underlying cause of a hemolytic anemia. In the diagram shown below, the oxygen dissociation curve for hemoglobin in his erythrocytes is compared with the curve obtained with normal red cells. 

Figure 7.11 shows the oxygen dissociation curve of one such hemoglobin, Hb Rainier, where it is seen that this hemoglobin is still 50% saturated with oxygen at a p02 of about 12 mm Hg compared to 27 mm Hg in normal hemoglobin. The value of n in the Hill equation is 1.5 for this hemoglobin. 

A very intriguing aspect of comparative biochemistry is the comparison of dissociation curves of hemoglobin (as a function of decreasing oxygen tension) with the general behavior of the corresponding animal species. 

The microcirculation is adapted to a specific distribution of oxygen tension (pOj) that is in part determined by the shape of the oxygen dissociation curve for hemoglobin. In this system, blood with specific pOj locates at specific microvascular sites as a result of the control of active mechanisms that sense pOj in tissue and blood, and partition oxygen delivery between the arteriolar and capillary circulation [44]. 

The pOj in blood is distributed so that the oxygen dissociation curve for hemoglobin has the steepest slope in the arterioles where the adrenergic sensor system has the highest density [76]. Arterioles ahead of this fulcrum deliver most of the oxygen to the tissues at rest. Capillary oxygen delivery becomes predominant in working tissue [78]. 

Figure 2-4. Oxygen dissociation curve for adult hemoglobin (HbA) demonstrating the characteristics of allosteric positive comparativity. Right shift of the curve caused by het-erotrophic ligands and increased temperature leads to decreased oxygen affinity.

The observation by Chanutin and collaborators (CIO, S64) and by Benesch and Benesch (B25, B26) that 2,3-DPG (and also ATP and inositol hexaphosphate, or IHP) binds to hemoglobin resulting in a shift to the right of the oxygen dissociation curve has led to numerous reports which describe topics related to biochemical and medical aspects of the... 

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