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.
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).