Difference Between Globin and Globulin

The main difference between globin and globulin is that globin is a superfamily of heme-containing globular proteins whereas globulin is a family of globular proteins with a higher molecular weight. Furthermore, globin is water-soluble while globulin is insoluble in pure water but, dissolves only in dilute salt solutions. 

Globin and globulin are two types of proteins found dissolved in the plasma. The levels of these proteins indicate disease conditions in different organ systems. Furthermore, the two prominent globins are myoglobin and hemoglobin while alpha 1 globulins, alpha 2 globulins, beta globulins, and gamma globulins are the major types of globulins. 

Key Areas Covered 

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

Key Terms 

Globin, Globulin, Hemoglobin, Myoglobin, Plasma Proteins

What is a Globin 

Globin is a protein which belongs to a superfamily of heme-containing globular proteins. Therefore, the main function of globins is to bind and/or transport oxygen. The two prominent forms of globins in the body are myoglobin and hemoglobin. Here, myoglobin is the oxygen-binding protein in the muscle tissue of vertebrates. In contrast, hemoglobin is the oxygen-transporting metalloprotein in red blood cells of vertebrates. In addition, it occurs in tissues of some invertebrates. Moreover, both of these proteins contain a heme prosthetic group, which reversibly binds to oxygen.

Figure 1: Hemoglobin – Alpha Chain

Furthermore, the main structural feature of all types of globins is their globin fold, which consists of a series of eight alpha-helical segments. Also, this is a three-dimensional fold. However, these eight helices share a specific nonlocal structure in the core. Generally, this specific structure contains amino acids close to each other in both their primary structure as well as in the space. Moreover, the average packing angle is 50 degrees. Meanwhile, the other six types of globins that occur in vertebrates are androglobin, cytoglobin, globin E, globin X, globin Y, and neuroglobin. 

What is a Globulin 

Globulin is a family of globular proteins, which have a higher molecular weight than albumins. Generally, albumins are globular proteins, but they are not globulins due to their low molecular weight. However, due to their high molecular weight, globulins do not dissolve in pure water. But, they dissolve in dilute salt concentrations. On the other hand, liver, as well as the immune system, produce globulins. Moreover, the four categories of globulins include alpha 1 globulins, alpha 2 globulins, beta globulins, and gamma globulins. A group of gamma globulins is known as immunoglobulins or antibodies. Furthermore, the serum level of globulins is 2.6-3.5 g/dL. 

Figure 2: Immunoglobulin

Moreover, alpha globulins have the lowest molecular weight among globulins. Their molecular weight is around 93 kDa. In contrast, gamma globulins have the highest molecular weight, which is around 1193 kDa. Furthermore, vicilin and legumin are the two types of globulins that occur in legumes. In addition, their function is to serve as storage proteins.  

Similarities Between Globin and Globulin  

• Globin and globulin are two types of proteins in the plasma. 
• They dissolve in water under different conditions. 
• Moreover,  they perform important functions in the blood. 

Difference Between Globin and Globulin 

Definition 

Globin refers to a superfamily of heme-containing globular proteins responsible for the binding and transport of oxygen while globulin refers to a family of simple proteins soluble in salt solutions and forming a large fraction of blood serum proteins. 

Examples 

The two prominent globins are myoglobin and hemoglobin while alpha 1 globulins, alpha 2 globulins, beta globulins, and gamma globulins are the major types of globulins. 

Function 

While the main function of globins is to bind and/or transport oxygen, globulins are serum proteins produced in the liver and by the immune system. 

Molecular Weight 

Moreover, the molecular weight of globins is around 16 kDa while the molecular weight of globulins is around 100-1000 kDa. 

Solubility 

Furthermore, globin is water-soluble while globulin is insoluble in pure water but, dissolves only in dilute salt solutions. 

Conclusion 

Globin is a group of proteins in the blood with a lower molecular weight. Moreover, they are the structural components of myoglobin and hemoglobin. Therefore, the main function of globins is to bind and transport oxygen. In contrast, globulin is a type of globular proteins in the blood. However, they have a higher molecular weight when compared to albumins. Furthermore, they have immune functions in the body. Therefore, the main difference between globin and globulin is their molecular weight and function. 

References:

1. “Globin.” Globin – an Overview | ScienceDirect Topics, Available Here.
2. Baron, Adrianne. “What Are Globulins? – Definition & Types.” Study.com, Study.com, Available Here.

Image Courtesy:

1. “PDB 1xz5 EBI” By Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute (Public Domain) via Commons Wikimedia   
2. “Structure of antibody molecule” By Inbal Sela-Culang, Vered Kunik, Yanay Ofran – The structural basis of antibody-antigen recognition. Front. Immunol., 08 October 2013 (CC BY-SA 4.0) via Commons Wikimedia