Difference Between Albumin and Globulin

The main difference between albumin and globulin is that albumin is the key protein in the blood, which regulates the osmotic pressure of blood whereas globulin is the second abundant type of proteins in the blood and is important in liver function, blood clotting, and fighting infections. Furthermore, albumin is soluble in pure water while globulin is insoluble in pure water. 

Albumin and globulin are the two main types of small protein in the blood called serum proteins. They have unique functions in the body. 

Key Areas Covered 

1. What is Albumin
     – Definition, Facts, Role
2. What is Globulin
     – Definition, Facts, Role
3. What are the Similarities Between Albumin and Globulin
     – Outline of Common Features
4. What is the Difference Between Albumin and Globulin
     – Comparison of Key Differences

Key Terms 

Albumin, Globulin, Immunoglobulins, Osmotic Pressure, Plasma Proteins

What is Albumin 

Albumin is a small protein, which makes up more than half of the total serum protein content of the blood. It is produced in the liver. Around 30-40% of the total albumin of the body occurs in the intravascular compartment while the rest occurs in the extravascular compartment and interstitial spaces. The diffusion of albumin from the serum does not occur freely. Therefore, albumin is critical in providing colloid osmotic or oncotic pressure, which is important in the regulation of the movement of water and solutes across the capillary walls.  Inside the vascular compartment, Albumin always bears a negative charge due to the presence of Na⁺ ions. The binding of Cl^– ions into albumin increases its negative charge, which in turn, increases the ability to retain more Na⁺ ions. This increases the number of molecules in the serum, exerting a 50% greater osmotic pressure than it would be by protein concentration alone.

Figure 1: Serum Albumin Structure

In addition, albumin helps in the transport of hormones, bilirubin, vitamins, metals, and drugs. It facilitates the fat metabolism by keeping the fat soluble in the serum as well.  

What is Globulin 

Globulin is a collective name for hundreds of small serum proteins, which can be enzymes, carrier proteins, complement proteins, immunoglobulins, etc. Most globulins are produced in the liver. But immunoglobulins are produced by the plasma B cells. Based on the migratory pattern of globulins during electrophoresis, four groups of globulins can be identified: α1, α2, β, and γ. Immunoglobulins mainly belong to the γ region. 

Figure 2: Serum Protein Electrophoresis

Globulin is the second most abundant type of serum proteins. The increase of globulin level in the serum is mainly due to the increase of immunoglobulins, which indicates pathogenic infections. Malnutrition may decrease the levels of globulins in the serum.  

Similarities Between Albumin and Globulin 

• Albumin and globulin are the two main types of serum proteins. 
• They have low molecular weights. 
• Most of them are produced in the liver. Malnutrition can decrease the levels of albumin and globulin in the serum. 
• Both have unique functions in the body.  
• They can be coagulated by heat. 

Difference Between Albumin and Globulin
Definition 

Albumin refers to a simple form of protein found in egg white, milk, and (in particular) blood serum while globulin refers to any group of simple proteins soluble in salt solutions, forming a large fraction of blood serum protein. 

Original Levels 

The level of serum albumin is 3.5-5.0 g/dL while the level of serum globulin is 2.5-4.5 g/dL.  

Types 

Albumin is a single protein while globulin is a group of serum proteins.  

Molecular Mass 

The molecular mass of albumin is 66.5 kDa while the molecular mass of globulin is comparatively higher than albumin. 

Solubility 

Albumin is soluble in water while globulin is only soluble in ammonium sulfate. 

Role 

Albumin is important in increasing the osmotic pressure of the blood while globulin can be enzymes, carrier proteins, complement proteins or immunoglobulins. This is an important difference between albumin and globulin.

Clinical Significance 

The level of albumin in the serum only increases in acute dehydration while the level of globulin in the serum mainly increases due to the increasing immunoglobulin. 

Conclusion 

Albumin is the most abundant serum protein, which is important in maintaining the osmotic pressure of the blood. However, globulin is a group of small serum proteins, which can be enzymes, carrier proteins, complement proteins, immunoglobulins, etc. The main difference between albumin and globulin is their characteristics and role. 

Reference:

1. Busher, Janice T. “Serum Albumin and Globulin.” Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd Edition., U.S. National Library of Medicine, 1 Jan. 1990, Available Here

Image Courtesy:

1. “PDB 1bm0 EBI” By Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute – http://www.ebi.ac.uk/pdbe-srv/view/images/entry/1bm0600.png, displayed on http://www.ebi.ac.uk/pdbe-srv/view/entry/1bm0/summary (Public Domain) via Commons Wikimedia 
2. “Serum protein electrophoresis normal gamma” By Simon Caulton – Own work (CC BY-SA 3.0) via Commons Wikimedia