Key Difference – Oxygenated vs Deoxygenated Hemoglobin
Hemoglobin is a protein found in red blood cells, which carry oxygen from lungs to the body tissues and organs and carbon dioxide from body tissues and organs to the lungs. There are two states of hemoglobin: oxygenated and deoxygenated hemoglobin. The key difference between oxygenated and deoxygenated hemoglobin is that oxygenated hemoglobin is the state of hemoglobin bound with four oxygen molecules while the deoxygenated hemoglobin is the unbound state of hemoglobin with oxygen. Oxygenated hemoglobin is bright red in colour while deoxygenated hemoglobin dark red in colour.
CONTENTS
1. Overview and Key Difference
2. What is Hemoglobin
3. What is Oxygenated Hemoglobin
4. What is Deoxygenated Hemoglobin
4. Side by Side Comparison – Oxygenated vs Deoxygenated Hemoglobin
5. Summary
What is Hemoglobin?
Hemoglobin (Hb) is a complex protein molecule present in red blood cells which gives the typical shape to the red blood cell (round with narrow center). The key roles of Hb includes transporting oxygen from lungs to the body tissues, exchanging it with carbon dioxide and taking carbon dioxide from the body tissues to the lung and exchanging back with oxygen. Hemoglobin molecule contains four polypeptide chains (protein subunits) and four heme groups as shown in figure 01. Four polypeptide chains represent two alpha globulin chains and two beta globulin chains. Heme is an important porphyrin compound in hemoglobin molecule which has a central iron atom embedded inside. Each polypeptide chain of the hemoglobin molecule contains a heme group and an iron atom. The iron atom is vital for the transportation of oxygen and carbon dioxide in the blood and it is the main contributor of red colour of the red blood cells. Hemoglobin is also called as a mettaloprotein due to its incorporation of iron atoms.
Oxygen supply to tissues and organs is vital and essential. Cells obtain energy through aerobic respiration (oxidative phosphorylation) using oxygen as an electron acceptor. Production of energy is required for optimal cell metabolism and functions. Oxygen supply is facilitated by the hemoglobin proteins. Therefore hemoglobin is also known as oxygen carrying protein in the blood.
The low level of hemoglobin in blood called anemia. Anemia condition may cause several diseases. There are different reasons for low hemoglobin concentrations in the blood. Deficiency of iron is the main reason, while excessive dieting, unhealthy lifestyles, some diseases and cancers are also causes for the same.
Hemoglobin molecule has four oxygen binding sites associated with four Fe+2 atoms. One molecule of hemoglobin can carry a maximum of four molecules of Oxygen. Hence, hemoglobin can be saturated or unsaturated with oxygen. Oxygen saturation is the percentage of oxygen binding sites of hemoglobin occupied by the oxygen. In other words, it measures the fraction of oxygen saturated hemoglobin relative to total hemoglobin. These two states of the hemoglobin are known as oxygenated and deoxygenated hemoglobin.
Figure 1: Structure of Hemoglobin
What is Oxygenated Hemoglobin?
When hemoglobin molecules are bound and saturated with oxygen molecules, the combination of hemoglobin with oxygen is known as oxygenated hemoglobin (oxyhemoglobin). Oxygenated hemoglobin is formed during the physiological respiration (ventilation), when oxygen molecules bind with heme groups of the hemoglobin in red blood cells. Oxygenated hemoglobin production mainly happens in the pulmonary capillaries near to alveoli of the lungs where the gaseous exchange occurs (inhalation and exhalation). The affinity of oxygen binding to the hemoglobin is highly influenced by the pH. When the pH is high there is a high affinity of binding oxygen to hemoglobin but it decreases as the pH decreases. There is normally a high pH in lungs, and a low pH in muscles. Thus, this difference in pH conditions is useful for oxygen attachment, transportation and release. Since there is a high binding affinity near the lung, oxygen binds with hemoglobin and make oxyhemoglobin. When oxyhemoglobin reaches the muscle due to low pH, it dissolves and releases oxygen to the cells. Normal oxygen level in blood of humans are considered to be in the range of 95 – 100 %. Oxygenated blood is visible in bright red (crimson red) colour. When the hemoglobin is in the oxygenated form, it is also known as R state (Relaxed state) of the hemoglobin.
Figure 2: Oxygenated hemoglobin
What is Deoxygenated Hemoglobin?
Deoxygenated hemoglobin is the form of hemoglobin that is not bound to oxygen. Deoxygenated hemoglobin lacks oxygen. Hence this state called T state (Tense state) of hemoglobin. Deoxygenated hemoglobin can be observed when oxygenated hemoglobin releases oxygen and it is exchanged with carbon dioxide near the plasma membrane of muscle cells where there is a low pH environment. When hemoglobin has a low affinity towards the oxygen binding, it delivers oxygen and convert into deoxygenated hemoglobin.
Figure 3: Oxygenated and deoxygenated blood flow through the body
What is the difference between Oxygenated and Deoxygenated Hemoglobin?
Oxygenated vs Deoxygenated Hemoglobin |
|
| Oxygenated hemoglobin is the combination of hemoglobin plus oxygen. | The unbound form of hemoglobin with oxygen is known as deoxygenated hemoglobin. |
| State of Oxygen Molecule | |
| Oxygen molecules are bound to hemoglobin molecule. | Oxygen molecules are not bound to hemoglobin molecule. |
| Color | |
| Oxygenated hemoglobin is bright red in color. | Deoxygenated hemoglobin is dark red in color. |
| State of Hemoglobin | |
| This is known as the R state of hemoglobin. | This is known as the T (tense) state of Hemoglobin. |
| Formation | |
| Oxygenated hemoglobin is formed when oxygen molecules bind with heme groups of the hemoglobin in red blood cells during the physiological respiration. | Deoxygenated hemoglobin is formed when oxygen is released from oxygenated hemoglobin and is exchanged with carbon dioxide near the plasma membrane of muscle cells. |
Summary – Oxygenated and Deoxygenated Hemoglobin
Hemoglobin is a vital protein found in red blood cells which is capable of carrying oxygen from the lung to the body tissues and bringing carbon dioxide from the body tissues to the lung. There are two states of hemoglobin due to the binding of oxygen. Those are oxygenated hemoglobin and deoxygenated hemoglobin. Oxygenated hemoglobin is formed when oxygen molecules attached to the Fe atoms. Deoxygenated hemoglobin is formed when oxygen molecules are released from the hemoglobin molecule. This is the key difference between oxygenated and deoxygenated Hemoglobin. Oxygen attachment and release is mainly influenced by the pH and the partial pressure of the Oxygen.
Reference:
1. Thomas, Caroline, and Andrew B. Lumb. “Physiology of haemoglobin.” Physiology of haemoglobin | BJA Education | Oxford Academic. Oxford University Press, 15 May 2012. Web. 20 Feb. 2017.
2. Marengo-Rowe, Alain J. “Structure-function relations of human hemoglobins.” Proceedings (Baylor University. Medical Center). Baylor Health Care System, July 2006. Web. 20 Feb. 2017
Image Courtesy:
1. “1904 Hemoglobin” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia
2. “Figure 39 04 01” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
3. 2101 Blood Flow Through the Heart” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia