Hemoglobin, oxygen dissociation

A 72-year-old woman with emphysema presents to the emergency room with fatigue and respiratory distress. Which set of arterial blood gas values below would represent her condition and reflect a shift of the hemoglobin oxygen dissociation curve to the right ... 

THE OXYGEN DISSOCIATION CURVES FOR MYOGLOBIN HEMOGLOBIN SUIT THEIR PHYSIOLOGIC ROLES... 

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. 

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). 

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. 

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.

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