The binding of oxygen with myoglobin and haemoglobin is a critical physiological process that underlies the efficient transport and delivery of oxygen to tissues throughout the human body. Understanding the factors that influence this binding capacity is essential for comprehending the intricacies of oxygen transport and utilization. This introductory exploration will delve into the key factors affecting the oxygen-binding capacity of myoglobin and haemoglobin, shedding light on the molecular mechanisms that govern oxygen delivery to cells and tissues.
Haemoglobin’s tetrameric structure, cooperative oxygen binding, and cooperative behavior make it a linchpin in the intricate orchestration of oxygen transport and systemic homeostasis. This article includes factors affecting binding of oxygen with Mb and Hb. Such as Partial pressure, temperature, Bohr effect, Haldane effect and other Ligands.
Table of Contents
Factors Affecting Binding of Oxygen with Myoglobin & Haemoglobin
1. Effect Of Partial Pressure
The most crucial factor affecting oxygen binding capacity is the partial pressure of oxygen in the surrounding environment. As partial pressure of O2 increases, the affinity of both myoglobin and haemoglobin for oxygen also increases, resulting in increased oxygen binding.
The function of Hemoglobin is to bind oxygen in the lungs (at high O2 partial pressure) & to carry it without any loss & release it to myoglobin in the cellular tissues (at low O2 partial pressure).
This implies that Myoglobin should have a greater affinity for oxygen at low partial pressure, The Oxygenation saturation curves for Hb & Mb is shown in the figure.
The degree of saturation for Mb is higher than for Hb at low partial pressures as shown by the comparison of the saturation curves for Mb & Hb at various partial pressures. For Mb, the curve is Hyperbolic & for Hb, the curve is sigmoidal. The shape of the curve is explained in terms of the equilibrium Mb + O2 ↔ MbO2
where, p is the partial pressure of oxygen.
The fractional oxygen saturation α is the ratio of the concentration of Mb present as MbO2 to the total concentration of Mb.
It follows that,
Mb curve only conforms to this equation but not the Hb curve.
2. Temperature
Temperature can influence the binding capacity of both myoglobin and haemoglobin. Higher temperatures often lead to decreased oxygen binding affinity. However, the effect of temperature varies between species.
3. pH (Bohr effect)
pH levels can affect the oxygen binding capacity in Haemoglobin i.e Hb is pH dependent whereas Mb is pH independent. In tissues, the decomposition of carbohydrate takes place. CO2 gas is released which is hydrolysed to carbonic acid & the concentration of H+ increases and hence pH decreases. Lower pH (more acidic conditions) decrease the affinity of haemoglobin for oxygen that is oxygen is released more readily in cells where metabolism is active & consequently a high concentration of CO2 at low pH. The response of Haemoglobin with change in pH is known as the Bohr effect. To know more about the Bohr effect check our article The Bohr Effect Illuminating Oxygen’s Dance in the Blood.
Reaction of Bohr effect
To get more concentration of H+ .CO2 should be more.
Conversely, higher pH (more alkaline conditions) increase the affinity of haemoglobin for oxygen. The O2 binding efficiency of Hb is maximum at pH 7.4. At pH 7.2 & 10 torr O2 partial pressure the extent of O2 binding is high for Mb & low for Hb. Check a small video on Bohr effects.
4. Carbon Dioxide Levels (Haldane effect)
Elevated CO2 levels in tissues can promote oxygen release from haemoglobin, facilitating the removal of CO2 as bicarbonate ions, which helps maintain pH balance. Increased levels of carbon dioxide can decrease the affinity of haemoglobin for oxygen. This is known as the Haldane effect. In tissues with high CO2 concentration, haemoglobin tends to release oxygen more readily. To learn more about the Haldane effect check our article, Haldane Effect A Key Player in Blood Gas.
5. Other Ligands
Myoglobin and haemoglobin can also bind to other molecules besides oxygen, such as carbon monoxide (CO). Carbon monoxide has a much higher affinity for these proteins than oxygen, which can interfere with their oxygen-binding capacity.
The binding capacity of gases with Hb is CN– = NO ~ CO > H2 > O2 > CO2 > N2 . CN– ,NO & CO can lead to death.
Cooperative Behavior
Cooperative behavior in haemoglobin is a remarkable phenomenon essential for efficient oxygen transport in vertebrates. Haemoglobin’s tetrameric structure allows it to bind to and transport large quantities of oxygen efficiently. Each subunit of haemoglobin contains a heme group, similar to myoglobin, but in hemoglobin, the binding of oxygen is cooperative.
As the first oxygen molecule binds to a heme group, it induces a conformational change that enhances the affinity of the remaining subunits for oxygen. This means that once one oxygen molecule is bound, it becomes easier for subsequent molecules to bind, creating a positive feedback loop. This cooperative behavior allows hemoglobin to pick up oxygen in the lungs, where oxygen levels are high, and release it readily in tissues where oxygen is needed. It ensures that oxygen is efficiently delivered to active muscles and organs, optimizing oxygen utilization throughout the body.
In contrast, myoglobin does not exhibit cooperativity; it has a hyperbolic oxygen-binding curve, indicating that its subunits do not influence each other’s oxygen-binding behavior. Myoglobin’s function is focused on oxygen storage and local oxygen release within muscle cells, where cooperative behavior is not required for its function