Myoglobin Structure and Function
Oxygen-Hemoglobin Dissociation Curve
In this tutorial, we will discuss how the concentration of oxygen in the blood plasma (partial pressure of O2 or pO2) affects oxygen-hemoglobin (O2-Hb) saturation.
- As O2 enters the vial of blood, the plasma pO2 increases and more O2 binds with hemoglobin.
Hb + O2 <———–>HbO2
- The reaction also causes the color of the RBCs in the vial to change from purple to red.
- As the pO2 approaches 100 torrs (or mmHg), the hemoglobin molecules become nearly fully saturated.
Hb + 1 O2 = 25% saturation
Hb + 2 O2 = 50% saturation
Hb + 3 O2 = 75% saturation
Hb + 4 O2 = 100% saturation
The O2-Hb relationship is sigmoidal (or s-shaped) and not linear. (see the image below)
The upper end of the curve is flatter than the lower end.
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This indicates that the first three O2 bind to hemoglobin molecules at relatively low pO2 (= 0 – 40 torr). In contrast, adding the 4th O2 to hemoglobin moleculess requires a relatively high pO2 (= 40 – 100 torr).