The terms “deoxy form” and “oxy form” refer to the oxygenation states of haemoglobin and myoglobin, two proteins involved in oxygen transport in the body. Myoglobin and Haemoglobin are the proteins that are involved in oxygen storage and transport in the body. They both contain a heme group, which is a complex of iron and porphyrin, responsible for binding to oxygen. The iron in the heme group can exist in different oxidation states, leading to the formation of deoxy and oxy forms. The deoxy and oxy forms of haemoglobin and myoglobin have distinct characteristics and functions. Here are some distinguishing points between the two forms.
Table of Contents
Deoxy form of haemoglobin/myoglobin
Deoxyhaemoglobin and deoxymyoglobin are the deoxygenated forms of haemoglobin and myoglobin, respectively.
- Location: Deoxyhaemoglobin is predominantly found in tissues with lower oxygen levels, such as muscles whereas Deoxymyoglobin is found in muscles where it serves as an oxygen reservoir.
- Iron State: In the deoxygenated state, the iron atom at the center of the heme group is in the ferrous (Fe2+) state and is High Spin.
- Oxygen Binding: Lacks bound oxygen, as it is in the low-oxygen state.
- Color: The color of deoxyhaemoglobin and deoxymyoglobin is generally purplish or dark red.
- Role: Deoxyhaemoglobin acts as a reservoir for oxygen release in tissues where oxygen demand is higher, such as during exercise or in areas with poor blood circulation. Deoxymyoglobin stores oxygen in muscle tissues, releasing it when needed for aerobic metabolism during muscle activity.
- Ligands: The primary ligands in deoxyhaemoglobin/deoxymyoglobin are water molecules (H2O) and a proximal histidine residue. The iron is coordinated with the above ligands in the absence of oxygen. The absence of oxygen in the heme iron results in the coordination of these ligands.
- Crystal Field Stabilization Energy: a term used in coordination chemistry to describe the energy difference between two electronic configurations of metal ions in a complex. CFSE arises from the electrostatic interactions between the electrons in the d orbitals of a metal ion and the ligands surrounding it. CFSE of deoxy form of Hb & Mb is -0.4Δo (low CFSE)
8. Magnetic Behavior: The fe atom in the deoxy form is paramagnetic in nature as it contains 4 unpaired electrons that can align with an external magnetic field and is ESR active.
9. Ionic Radius of Fe: The ionic radius of iron is more as the CFSE value is less i.e.
10. Bond Distance: The Fe-N bond distance is more and therefore it gets out of the plane (Tensed State).The Fe is about 0.4 Ao above the plane of Porphyrin ring.
Oxy form of haemoglobin/myoglobin
Oxyhaemoglobin and oxymyoglobin are the oxygenated forms of haemoglobin and myoglobin, respectively. Both play crucial roles in the transport and storage of oxygen in the body.
- Location: Oxyhaemoglobin is predominantly found in the lungs, where oxygen is bound whereas Oxymyoglobin is found in muscles, storing oxygen for muscle use.
- Iron State: In the oxygenated state, when oxygen binds to the iron in the heme group, the iron becomes ferric (Fe3+) and is low spin.
- Oxygen Binding: Molecular oxygen (O2) is bound to the iron, indicating a high-oxygen state. The oxygen binds in the superoxide form to Hb & Mb and have stretching frequency of approximate 1100cm-1.
- Color: The binding of oxygen causes a change in color, making oxyhaemoglobin and oxymyoglobin appear bright red.
- Role: Oxyhaemoglobin is found in the lungs, transporting oxygen from the lungs to tissues. Oxymyoglobin is found in muscle tissues and serves as an oxygen reservoir for the muscle cells. It releases oxygen when the muscles require it during periods of increased activity.
- Ligands: The primary ligand in oxyhaemoglobin is molecular oxygen (O2), which binds to the iron atom in the heme group. The heme group, which is a complex of iron and a porphyrin ring, is the site where oxygen binds to these proteins.
- Crystal Field Stabilization Energy: CFSE of oxy form of Hb & Mb is -2.0Δo (high CFSE)
8. Magnetic Behavior: oxy form of Hb & Mb are diamagnetic. Diamagnetic substances have no unpaired electrons, and they are weakly repelled by an external magnetic field. The unpaired electron which is there undergoes Antiferromagnetic coupling.
9. Ionic Radius of Fe: The ionic radius of iron is less as the CFSE value is more.
10. Bond Distance: The Fe-N bond distance is less and therefore Fe atom sits in the plane (Relaxed State).
Conformational changes in Deoxy Form And Oxy Form
When oxygen binds to the heme iron, it causes a conformational change in haemoglobin, leading to the transition from the T (tense) state (deoxyhaemoglobin) to the R (relaxed) state (oxyhaemoglobin). Similar to haemoglobin, the binding of oxygen induces a conformational change in myoglobin, allowing it to function as an oxygen reservoir in muscle tissues.
Binding Capacity of Oxygen
The binding and release of oxygen by haemoglobin are dynamic processes that are influenced by factors such as oxygen concentration, pH, and carbon dioxide levels. The ability of haemoglobin to bind and release oxygen is crucial for its role in transporting oxygen from the lungs to tissues and organs throughout the body. For more information about
The binding and release of oxygen by haemoglobin are dynamic processes that are influenced by factors such as oxygen concentration, pH, and carbon dioxide levels. The ability of haemoglobin to bind and release oxygen is crucial for its role in transporting oxygen from the lungs to tissues and organs throughout the body. For more information about factors Affecting Binding of Oxygen, please refer the webpage Oxygenation Dynamic, Binding of Oxygen with Myoglobin & Haemoglobin & Cooperative.
Both deoxyhaemoglobin and deoxymyoglobin represent states where oxygen has been released from the heme group, and the iron is in the ferrous state. These deoxygenated forms are essential for the storage and delivery of oxygen to tissues and organs as needed, depending on the oxygen demands of the body at a given time. The transition between the oxygenated and deoxygenated forms is crucial for the efficient transport and utilization of oxygen in the body.
In the lungs, where oxygen levels are high, haemoglobin binds to oxygen (forming oxyhaemoglobin). In tissues with lower oxygen levels, such as muscles, haemoglobin releases oxygen (forming deoxyhaemoglobin). Myoglobin, found in muscles, serves a similar purpose by storing oxygen and releasing it when needed for aerobic metabolism during muscle activity.
Summary of Deoxy Form And Oxy Form
In summary, the key differences lie in their colors, oxygen-binding states, iron oxidation states, role and locations within the body. Deoxy form are associated with low oxygen levels, while oxy forms are linked to high oxygen levels and play crucial roles in oxygen transport and storage.
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