Oxygen & HCO3- Binding: Human vs Crocodile Hemoglobin

[Momentum09]

I was given the oxygen binding curves for human and crocodile hemoglobins, with the crocodile having a higher affinity for oxygen at p50.
My questions are,
1) Crodocile hemoglobin does not bind BPG. Instead, deoxyhemoglobin preferentially binds to HCO3-. How does bicarbonate binding affect the p50 of crocodile hemoglobin binding to oxygen?
2) How does the crocodile deoxyhemoglobin's affinity for HCO3- help it feed?

Can someone please give me hints as to how to approach this problem? If you can explain the concepts to me that would be great!
Thank you so much!

 

[Nino MMP]

1) Bicarbonate binding to deoxyhemoglobin increases the p50 of oxygen binding by reducing the affinity of hemoglobin for oxygen. This is because the bicarbonate molecule competes with oxygen for binding sites on the hemoglobin, resulting in a decrease in the oxygen-binding affinity of the hemoglobin. As such, the p50 of oxygen binding is increased as oxygen molecules have to reach higher concentrations to be able to displace the bicarbonate molecules from the hemoglobin.2) The ability of crocodile deoxyhemoglobin to bind HCO3- is thought to be an adaptation to the low oxygen concentrations in the water they inhabit. By binding bicarbonate, the crocodile hemoglobin can increase its affinity for oxygen, allowing it to more effectively extract oxygen from the water. This helps the crocodile feed by allowing it to stay submerged for longer periods of time and access more oxygen to fuel its activities.

 

[Blueshift5]

I can provide some insights into the questions you have raised regarding oxygen and HCO3- binding in human and crocodile hemoglobins.

1) Bicarbonate (HCO3-) is known to be a major regulator of oxygen binding in hemoglobin. In human hemoglobin, BPG (2,3-bisphosphoglycerate) is the main regulator, while in crocodile hemoglobin, HCO3- takes on this role. This is due to the fact that crocodile hemoglobin does not have a binding site for BPG, but instead has a binding site for HCO3-.

The binding of HCO3- to deoxyhemoglobin in crocodiles leads to a decrease in the p50 value, meaning that the affinity for oxygen increases. This is because the binding of HCO3- stabilizes the T state of the hemoglobin, which is the deoxygenated form with a lower affinity for oxygen. This allows the crocodile hemoglobin to hold onto oxygen more tightly, making it more efficient at oxygen uptake and delivery.

2) The affinity of crocodile deoxyhemoglobin for HCO3- plays an important role in their feeding behavior. Crocodiles are semiaquatic animals, spending a significant amount of time both in water and on land. When they are submerged in water, they rely on their deoxyhemoglobin to bind to HCO3- and release oxygen, allowing them to stay submerged for longer periods of time while hunting for prey. This is especially important for crocodiles living in areas with low oxygen levels in the water.

Additionally, the increased affinity for HCO3- in crocodile deoxyhemoglobin also allows them to survive in environments with high levels of carbon dioxide. This is because HCO3- can bind to and neutralize excess carbon dioxide, preventing it from building up in the body and causing acidosis.

In summary, the difference in oxygen and HCO3- binding between human and crocodile hemoglobins is due to their unique physiological adaptations. The binding of HCO3- in crocodile hemoglobin not only affects the p50 value, but also plays a crucial role in their survival and feeding behavior in their natural habitat.