What is the Difference Between Hemoglobin and Hemoglobin A1c

The main difference between hemoglobin and hemoglobin A1c is that the hemoglobin is the iron-containing metalloprotein in the red blood cells of nearly all vertebrates whereas hemoglobin Alc is glycated hemoglobin A, which is a form of hemoglobin that is covalently bound to glucose.

Furthermore, hemoglobin and hemoglobin Alc are two types of globular proteins that circulate via blood. Wherein, the hemoglobin is responsible for the transport of oxygen while the main use of hemoglobin Alc is in the diagnostic test for diabetes and as an assessment test for glycemic control in people with diabetes.

Key Areas Covered

1. What is Hemoglobin
     – Definition, Structure, Importance
2. What is Hemoglobin Alc
     – Definition, Structure, Importance
3. What are the Similarities Between Hemoglobin and Hemoglobin A1c
     – Outline of Common features
4. What is the Difference Between Hemoglobin and Hemoglobin A1c
     – Comparison of Key Differences

Key Terms

Glycated Hemoglobin, Hemoglobin, Hemoglobin A, Hemoglobin A1c, Oxygen Transport

What is Hemoglobin

Hemoglobin is a globular hemoprotein, containing a tightly bound prosthetic group known as heme. Here, heme is a complex of protoporphyrin IX and ferrous iron (Fe²⁺) where the ferrous iron is attached to the center of the heme molecule via four bonds with the nitrogens of the porphyrin ring. Also, this ferrous ion can form two additional bonds on each side of the porphyrin ring. One of these positions can be achieved by oxygen as coordinated to the side chain of a histidine residue. Apart from the heme group, hemoglobin molecule shows a tetrameric structure as it is made up of four polypeptide chains; two alpha and two beta chains.

Figure 1: Hemoglobin Structure

Furthermore, hemoglobin exclusively occurs in red blood cells. On that account, the main function of hemoglobin is to transport oxygen from the lungs to the tissues of the body through the blood. Also, it is responsible for the transport of carbon dioxide and protons from tissues to the lungs. Therefore, hemoglobin has a role in controlling blood pH. Moreover, in each day, 6-7 g of hemoglobin is produced by the body to replace the lost hemoglobin through its normal turn over. Anemia is the main disease condition associated with hemoglobin. In which, the decreased amounts of hemoglobin results in the decreased ability to transport oxygen. Also, hemoglobinopathies is a genetic disease associated with the abnormal structure of the hemoglobin molecule. Some of the mutations of hemoglobinopathies can also lead to sickle cell disease or thalassemia.

What is Hemoglobin Alc

Hemoglobin A1c is the glycated form of hemoglobin A. Here; the hemoglobin A is the major form of hemoglobin in humans synthesized after birth. Around 95% of hemoglobin of an adult human is hemoglobin A. However, some of the hemoglobin in the blood can undergo glycation, forming hemoglobin A1c. Here, the extent of glycation depends on the concentration of the hexose sugars; in other words, glucose in the plasma.

Figure 2: Glycation PAthway of a Protein

Moreover, hemoglobin A1c is the most common form of glycated hemoglobin in the blood. It is formed by the attachment of glucose residues to the beta globin chains of the hemoglobin A. Significantly, the patients with diabetes mellitus have increased amounts of hemoglobin A1c in the blood. Therefore, measuring glycated hemoglobin helps to monitor blood glucose levels during the last two months. Here, glycation brings permanent changes to the hemoglobin molecule, and this allows the measurement of glucose exposure of hemoglobin over a long period of time. However, it is limited to three months of time as the lifespan of red blood cell is around 120 days.

Similarities Between Hemoglobin and Hemoglobin A1c

• Hemoglobin and hemoglobin A1c are two types of globular hemoproteins.
• Both contain the tightly bound prosthetic group known as heme.
• Also, both occur in red blood cells.
• Furthermore, they are capable of binding different types of molecules such as oxygen, carbon dioxide or glucose.
• Besides, the main function of both types of hemoglobin is to transport molecules through the blood.

Difference Between Hemoglobin and Hemoglobin A1c

Definition

Hemoglobin refers to the red protein responsible for transporting oxygen in the blood of vertebrates while hemoglobin A1C refers to a minor component of hemoglobin to which glucose is bound. Thus, this is the main difference between hemoglobin and hemoglobin A1c.

Significance

Furthermore, hemoglobin is a tetramer composing of two identical dimers, (αβ)1 and (αβ)2 while hemoglobin A1c is the glycated hemoglobin A. Hence, this is an additional difference between hemoglobin and hemoglobin A1c.

Binding to

Also, another difference between hemoglobin and hemoglobin A1c is that the hemoglobin can bind to oxygen, carbon dioxide or carbon monoxide while hemoglobin Alc forms by the binding of glucose to the β-globin chains of hemoglobin A.

Role

Importantly, the main function of hemoglobin is to transport oxygen from the lungs to the body tissues while increased amounts of hemoglobin A1c occur in diabetes mellitus.

Importance

Besides, one other important difference between hemoglobin and hemoglobin A1c is that the defective hemoglobin can cause various diseases including anemia, hemoglobinopathies, etc., while hemoglobin A1c can be used to monitor blood glucose levels during the last two months.

Conclusion

Hemoglobin is a globular protein responsible for the transport of oxygen throughout the body. It is a tetramer made up of two alpha and beta chains. It contains a prosthetic heme group, which contains a ferrous ion. Whereas, the hemoglobin A1c is the glycated hemoglobin A. It contains bound glucose molecules to the beta chains, and it is increased under diabetic conditions. Therefore, the main difference between hemoglobin and hemoglobin A1c is their structure and function.

References:

1. Grigson, Vivian. “Hemoglobin Structure & Function – Ppt Video Online Download.” SlidePlayer, Available Here.

Image Courtesy:

1. “1904 Hemoglobin” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia   
2. “AGE accumulation” By Jasper Dijkstra (CC BY-SA 3.0) via Commons Wikimedia