Oxygen saturation curve, hemoglobin

The importance of the BPG effect is evident in Figure 15.35. Hemoglobin stripped of BPG is virtually saturated with Og at a pO of only 20 torr, and it cannot release its oxygen within tissues, where the jbOg is typically 40 torr. BPG shifts the oxygen saturation curve of Hb to the right, making the Hb an Og... 

FIGURE 6-29 Substrate-activity curves for representative allosteric enzymes. Three examples of complex responses of allosteric enzymes to their modulators, (a) The sigmoid curve of a homotropic enzyme, in which the substrate also serves as a positive (stimulatory) modulator, or activator. Note the resemblance to the oxygen-saturation curve of hemoglobin (see Fig. 5-12). (b) The effects of a positive modulator (+) and a negative modulator (—) on an allosteric enzyme in which K0 5 is altered without a change in Zmax. The central curve shows the substrate-activity relationship without a modulator, (c) A less common type of modulation, in which Vmax is altered and /C0.sis nearly constant. 

Be able to interpret oxygen saturation curves of various types of hemoglobins by relating such curves to their properties and describe how the release of 02 is affected. 

Binding of 02 to one heme group in hemoglobin increases the affinity for 02 of its other heme groups. This effect produces the sigmoidal oxygen saturation curve. 

Figure 2-13. Oxygen saturation curves for myoglobin and adult hemoglobin (HbA). Myoglobin has a hyperbolic saturation curve. HbA has a sigmoidal curve. The HbA curve shifts to the right at lower pH, with higher concentrations of 2,3-bisphosphoglycerate (BPG), or as C02 binds in the tissues. Thus, 02 is released more readily. P50 ( ) is the partial pressure of 02 at which HbA is half-saturated with 02.

Effect of 2,3-bisphosphoglycerate (2,3-DPG) on the oxygen saturation curve of hemoglobin. Note that 2,3-DPG decreases the affinity of hemoglobin for oxygen. 

Figure 1-1. Oxygen saturation curves for hemoglobin and myoglobin.

We have already mentioned that disturbance of BPG metabolism can affect oxygen binding by hemoglobin. Figure 6.9 shows the effect on oxygen saturation curves. 

Fig. 44.12. Effect of pH on oxygen saturation curves. As the pH decreases, the affinity of hemoglobin for oxygen decreases, producing the Bohr effect.

FIGURE 4.25 The oxygen saturation curves for myoglobin and for hemoglobin at five different pH values. 

R. Wootton and D. Bull, Biochem. Soc. Trans., 17, 559 (1989). BW316, a Dialdehyde Designed to Right-Shift the Oxygen Saturation Curve of Hemoglobin. 

Studies of oxygen transport in pregnant mammals have shown that the 02-saturation curves of fetal and maternal blood are markedly different when measured under the same conditions. Fetal erythrocytes contain a structural variant of hemoglobin, HbF, consisting of two a and two y subunits (a2y2), whereas maternal erythrocytes contain HbA (a2/32). 

HbA now has a greater affinity for oxygen than does HbF. When BPG is reintroduced, the 02-saturation curves return to normal, as shown in the graph. What is the effect of BPG on the 02 affinity of hemoglobin How can the above information be used to explain the different 02 affinities of fetal and maternal hemoglobin ... 

---