Question

Hemoglobin and Myoglobin, HOW is oxygen binding regulated? what other mechanisms control oxygen binding in oxygenated vs deoxygenated tissues ( lung v. exercising muscles)?  

Answer 1

Haemoglobin has relatively high affinity for dioxygen at a high partial pressure of dioxygen and myoglobin has relatively high affinity for dioxygen at the low partial pressure of dioxygen. Dioxygen enters the blood in the lungs where the partial pressure of dioxygen is high and haemoglobin is virtually saturated with dioxygen in the lungs. When haemoglobin carries dioxygen to the muscle tissues, it experiences the low partial pressure of dioxygen and its affinity for dioxygen has fallen off rapidly and in this situation, the affinity of myoglobin for dioxygen is relatively high. Therefore in muscle tissues, dioxygen is thermodynamically favourable transferred from haemoglobin to myoglobin.

Further, there is a co-operative effect in the case of haemoglobin. There are four subunits in the haemoglobin and binds with four dioxygen molecule. When first dioxygen binds with haemoglobin on the first subunit, it supports the binding of rest of the three dioxygen molecule on the remaining three subunits of haemoglobin. This effect is called Co-Operative Effect.

This Co-Operative Effect is dependent on pH in the body. The affinity of haemoglobin for dioxygen decreases with a decrease in pH. This is called Bohr effect. The CO₂ released in the muscle tissues is the end product of the breakdown of Glucose. CO₂ is acidic and thus decrease the pH in the tissues. The greater the muscular activity, greater the release of the CO₂ . Most of the CO2 transported to the lungs in the form of soluble bicarbonate ion (HCO₃^-) formed by carbonic anhydrase enzyme.

HCO₃^- ion takes up the proton from haemoglobin to form H₂CO₃ which then converted to CO₂ and H₂O by carbonic anhydrase enzyme and the CO₂ thus formed exhale out.