What is the Difference Between Leucine and Isoleucine

The main difference between leucine and isoleucine is that the leucine is important in general health of muscles as it stimulates protein synthesis and reduces the breakdown of proteins in muscles following physical trauma. On the other hand, isoleucine is essential for the production of hemoglobin and red blood cells, and it plays a role in detoxification of nitrogenous wastes such as ammonia inside the body. 

Leucine, isoleucine, and valine are the three branched chain amino acids (BCAAs), which are under the category of essential amino acids for the human body. In general, they play a key role in energy production, normal metabolism and health of the muscles, and for responding to stress. 

Key Areas Covered 

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

Key Terms 

BCAAs, Detoxification, Isoleucine, Leucine, Muscle Health

What is Leucine 

Leucine is one of the 20 essential amino acids required for the production of proteins. Generally, the dietary sources of leucine are meats, dairy products, soy, beans, and other legumes. Also, its side chain is an isobutyl group. Therefore, it is one of the three branched chain amino acids (BCAAs). The metabolic end products of leucine are the acetyl-CoA and acetoacetate. In addition, leucine and lysine are the two exclusively ketogenic amino acids. Moreover, leucine is the most important ketogenic amino acid in the body. 

Figure 1: L-Leucine

Furthermore, leucine plays an important role in the general health of the muscles. Also, it stimulates protein synthesis while reducing protein breakdown in muscles following physical trauma. In addition, it increases insulin levels in the blood, producing a similar effect on muscle recovery. On the other hand, it regulates blood sugar levels by acting as a source for gluconeogenesis, which is the process of synthesizing glucose from non-carbohydrate sources. Also, it helps in the healing of muscles and the body. 

What is Isoleucine 

Isoleucine is another essential amino acid, which is a structural isomer of leucine. Therefore, it contains the same number of carbon atoms, which is four in a different arrangement. That means; its side chain is a sec-butyl group. In general, isoleucine naturally occurs in plants and microorganisms. Its synthesis starts from pyruvic acid and alpha-ketoglutarate in bacteria. In addition, isoleucine is both ketogenic and glucogenic amino acid. Therefore, after its transamination with alpha-ketoglutarate, its carbon skeleton can be converted into succinyl CoA to incorporate into the TCA cycle. Also, isoleucine can be converted into oxaloacetate to incorporate into the gluconeogenesis pathway.

Figure 2: L-Isoleucine

Other than regulating glucose levels in the blood and helping in the process of wound healing as same as leucine, isoleucine has some other unique roles in the body. It takes part in the detoxification of nitrogenous wastes such as ammonia in the body, aiding their excretion through kidneys. Moreover, isoleucine is important in the production of red blood cells and hemoglobin. Thus, it is an important amino acid in recovering from blood loss and anemia.  

Similarities Between Leucine and Isoleucine 

• Leucine and isoleucine are two types of branched-chain amino acids (BCAAs). 
• However, they have a similar molecular formula, which is C6H13NO2. 
• Also, their molecular mass is 131.18 g/mol. 
• Both are hydrophobic amino acids. Also, they are non-polar and aliphatic amino acids.  
• Besides, both have a four-carbon side chain. But, their layout is different. Therefore, they are structural isomers.  
• Moreover, both are essential amino acids, which are proteogenic. 
• They are essential for the energy production and general metabolism of muscles. 
• Further, they are important for generating a physiological response to stress. 
• Significantly, both play a role in regulating blood sugar levels and wound healing. 

Difference Between Leucine and Isoleucine 

Definition 

Leucine refers to a white crystalline essential amino acid obtained by the hydrolysis of dietary protein such as of eggs, soy, or fish and plays an important role in various physiological functions, while isoleucine refers to a crystalline, hydrophobic, essential amino acid obtained in its levorotatory L-form by the hydrolysis of dietary protein and is isomeric with leucine. Thus, this is the main difference between leucine and isoleucine.

Other Names 

The other names for leucine are 2-Amino-4-methylpentanoic acid and isobutylglycine while the other names for isoleucine are 2-Amino-3-methylpentanoic acid and sec-butylglycine. 

Side Chain 

Another difference between leucine and isoleucine is that the leucine contains an isobutyl side chain, while isoleucine contains a sec-butyl side chain.  

Catabolism 

Moreover, Leucine is exclusively a ketogenic amino acid, while isoleucine is both glucogenic and ketogenic amino acid.  

Main Function 

Leucine is important in general health of muscles as it stimulates protein synthesis and reduces the breakdown of proteins in muscles, while isoleucine is essential for the production of hemoglobin and red blood cells and it plays a role in detoxification of the nitrogenous wastes such as ammonia inside the body. Functionally, this is the main difference between leucine and isoleucine.

Other Functions 

Furthermore, while leucine increases insulin levels in the blood and stimulates gluconeogenesis, helping to heal the body and muscles, isoleucine also regulates blood glucose levels and aid in wound healing. Hence, this is another functional difference between leucine and isoleucine.

Importance 

In addition, leucine is important for recovering after a physical trauma, while isoleucine is important for recovering from blood loss and anemia. 

Conclusion 

Leucine is an essential amino acid, which is hydrophobic and in the category of BCAAs. Moreover, it is important in recovering after a muscle trauma as it increases protein synthesis while reducing protein breakdown. On the other hand, isoleucine is a structural isomer of leucine, and it is also an essential amino acid in the BCAAs category. However, it plays a role in the production of hemoglobin and red blood cells. Hence, it is important for recovering from blood loss. However, both leucine and isoleucine are important for regulating blood glucose levels and wound healing. Thus, the main difference between leucine and isoleucine is their unique functions.    

References:

1. Davis, Jack. “What Are Leucine and Isoleucine?” NEW MEDICAL LIFE SCIENCES, 27 Feb. 2019, Available Here.

Image Courtesy:

1. “L-Leucine” By Harbin – Own work (Public Domain) via Commons Wikimedia   
2. “L-Isoleucin – L-Isoleucine” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia