Difference Between Ferritin and Hemoglobin

The main difference between ferritin and hemoglobin is that ferritin is an intracellular protein that stores iron inside the cell, whereas hemoglobin is the iron-containing, oxygen-transport metalloprotein that occurs in red blood cells. Furthermore, ferritin is a universal protein that occurs in all types of organisms, while hemoglobin occurs in the red blood cells of all vertebrates and tissues of invertebrates.  

Ferritin and hemoglobin are two types of iron-containing proteins that occur in different types of organisms. Generally, low levels of these proteins in the body cause anemia. 

Key Areas Covered 

1. What is Ferritin
     – Definition, Structure, Function
2. What is Hemoglobin
     – Definition, Structure, Function
3. What are the Similarities Between Ferritin and Hemoglobin
     – Outline of Common Features
4. What is the Difference Between Ferritin and Hemoglobin
     – Comparison of Key Differences

Key Terms 

Anemia, Ferritin, Hemoglobin, Iron Storage, Oxygen Transport

What is Ferritin 

Ferritin is the main form of iron storage protein inside cells of almost all types of organisms, including animals, higher plants, algae, and bacteria. Generally, it occurs as a cytosolic protein in the cells of many tissues. However, a small amount of ferritin also occurs in the serum, functioning as an iron carrier. Besides, the apoferritin is a form of ferritin that is not bound to iron.

The main function of ferritin is to keep the iron in a soluble but non-toxic form. Furthermore, the structure of ferritin contains 24 subunits, which form a nanocage. Here, the core contains the stored iron molecules.

Figure 1: Ferritin

Furthermore, ferritin acts as a buffer which balances iron deficiency and iron overload. It is an indirect marker of total iron stored in the body. Thus, serum ferritin is an important blood test to diagnose iron-deficiency anemia. Especially, this test helps to distinguish between iron deficiency anemia from anemia of chronic disease. 

What is Hemoglobin 

Hemoglobin is an iron-containing metalloprotein which occurs in red blood cells of vertebrates. Therefore, it is the main form of oxygen-transporting protein of vertebrates, carrying oxygen from the lungs or gills to the metabolizing tissues of the body. Generally, 96% of the dry weight of the red blood cells of mammals accounts for hemoglobin. Moreover, the binding of hemoglobin into oxygen forms oxyhemoglobin. In contrast, hemoglobin binds to carbon dioxide, forming carbaminohemoglobin.

Figure 2: Hemoglobin

Moreover, the hemoglobin molecule consists of four protein subunits. Therefore, it is a tetramer. The type of subunits in the molecule determines the type of hemoglobin. Generally, the most common type of hemoglobin in adults is hemoglobin A (α2β2), comprises of two α and two β subunits. However, the type of hemoglobin in infants is hemoglobin F (α2γ2), comprising of 2 α chains and 2 γ chains. Meanwhile, each subunit of hemoglobin contains a non-protein, prosthetic heme group, which in turn consists of iron in a heterocyclic ring of porphyrin. 

Furthermore, the reduced amounts of hemoglobin cause anemia, decreasing the binding of oxygen into red blood cells. Genetic defects cause hemoglobin molecules with abnormal structures, resulting in hemoglobinopathies. Also, nutritional deficiencies, the loss of blood, problems in bone marrow, etc. also cause low hemoglobin levels. 

Similarities Between Ferritin and Hemoglobin  

• Ferritin and hemoglobin are two types of iron-containing proteins that occur in organisms. 
• Both are multi-subunit, globular proteins. 
• Besides, both contain iron in the form of Fe(II). 
• However,  low levels of these proteins can cause anemia. 
• Different types of blood tests are there to measure the levels of both types of proteins. 

Difference Between Ferritin and Hemoglobin 

Definition 

Ferritin refers to a universal protein inside cells which stores and releases iron while hemoglobin refers to the protein responsible for the transport of oxygen in the blood of vertebrates. 

Occurrence 

Ferritin is a universal protein that occurs in all types of organisms, while hemoglobin occurs in the red blood cells of all vertebrates and tissues of invertebrates.  

Structure 

Moreover, ferritin is a globular protein, comprising of 24 subunits, while hemoglobin is a globular protein, comprising of 4 subunits. 

Subunit Types 

The two types of protein subunits in ferritin are light (L) and heavy (H) types while the three types of subunits in different types of hemoglobin subunits are alpha, beta, delta, and gamma. 

Molecular Weight 

While the molecular weight of ferritin is 474 kDa, the molecular weight of hemoglobin is 64 kDa. 

Types  

The two types of ferritin based on the binding state of iron are ferritin and apoferritin, while the two types of hemoglobin-based on the binding of oxygen are oxyhemoglobin and deoxyhemoglobin. 

Importance 

Furthermore, ferritin is the major protein responsible for iron storage, while hemoglobin is the main protein responsible for the transport of oxygen through the blood. 

Normal Levels 

The normal levels of ferritin are 30–300 ng/mL for males and 18–160 ng/mL for females while the normal levels of hemoglobin are 13.5-17.5 g/dL for males and 12.0-15.5 g/dL for females. 

Deficiency 

Moreover, the ferritin test is important to identify iron deficiency anemia while blood tests for hemoglobin can reveal both anemia and hemoglobinopathies. 

Conclusion 

Ferritin is the main form of iron-storage protein, and it occurs inside cells of almost all types of organisms. Moreover, it is a globular protein with 24 subunits. It can release iron based on the requirements of the organism. On the other hand, hemoglobin is the main form of iron-containing, oxygen transport protein in vertebrates. In contrast, it is a globular protein with four subunits. However, low levels of both proteins cause anemia. Thus, the main difference between ferritin and hemoglobin is their structure and function.  

References:

1. “Hemoglobin and Functions of Iron.” UCSF Medical Center, Available Here.
2. Wilson, Debra Rose. “Ferritin Level Blood Test.” Healthline, Healthline Media, 8 Aug. 2017. Available Here.

Image Courtesy:

1. “Ferritin” (GPL) via Commons Wikimedia   
2. “1904 Hemoglobin” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia