What is the Difference Between Lysine and Leucine

The main difference between lysine and leucine is that lysine is a hydrophilic amino acid, while leucine is a hydrophobic amino acid.   

In brief, lysine and leucine are two types of amino acids that are essential for the human body. Both are aliphatic amino acids.

Key Areas Covered

1. What is Lysine
     – Definition, Structure, Function
2. What is Leucine
     – Definition, Structure, Function
3. Similarities Between Lysine and Leucine
     – Outline of Common Features
4. Difference Between Lysine and Leucine
     – Comparison of Key Differences

Key Terms

Leucine, Lysine

What is Lysine

Lysine is a proteogenic amino acid that is a precursor of many proteins. It is a basic amino acid with a side chain containing an amine group. The side chain of lysine is a lysyl ((CH₂)₄NH₂) group. It is a hydrophilic amino acid. Lysine is an essential amino acid for the body as it is not synthesized inside the body. Therefore, it should be obtained from the diet. Meat, cheese, eggs, certain fish like cod and sardines, spirulina, fenugreek seeds, and soybeans are some sources of lysine. Legumes are the best source of lysine for vegans.

Figure 1: L Lysine

Most importantly, lysine is a proteogenic amino acid involved in crosslinking of collagen peptides. It also helps in uptaking essential mineral nutrients and in the production of carnitine. In addition to that, lysine has an impact on epigenome involvement in histone modifications. Furthermore, people who lack lysine can experience fatigue, nausea, dizziness, loss of appetite, agitation, bloodshot eyes, and slow growth. The lack of lysine can also cause several disease statuses, including defective connective tissues, impaired fatty acid metabolism, and systemic protein-energy deficiency.

What is Leucine

Leucine is another essential amino acid for the human body that needs to be taken from the diet. Most meat, dairy products, soybeans, beans, and legumes contain leucine. It is a proteogenic amino acid. Therefore, it is an alpha amino acid containing a side chain of the isobutyl group. It is also a nonpolar aliphatic amino acid. In addition, it is a hydrophobic amino acid. Like other amino acids, valine, and isoleucine, leucine is a branched amino acid (BCAA). They are important in giving energy to muscles during exercises. Along with lysine, leucine is an exclusively ketogenic amino acid. Its metabolic end products include acetyl Co-A and acetoacetate.

Figure 2: L Leucine

Moreover, leucine increases muscle growth and body mass. It also may increase the levels of human growth hormone. It helps to control blood sugar. A very high dose of leucine may cause low blood sugar (hypoglycemia). Also, it causes pellagra with symptoms of skin lesions, hair loss, and gastrointestinal problems. Supplements of leucine are not recommended for pregnant women.

Similarities Between Lysine and Leucine

• Lysine and leucine are two types of essential amino acids for the human body.
• Both are aliphatic amino acids.
• They are important in proteogenesis.
• They are exclusively ketogenic amino acids.

Difference Between Lysine and Leucine

Definition

Lysine refers to a basic amino acid that is a constituent of most proteins, an essential nutrient in the diet of vertebrates, while leucine refers to a hydrophobic amino acid that is a constituent of most proteins, also an essential nutrient in the diet of vertebrates.

Characteristics                      

Lysine is a hydrophilic amino acid, while leucine is a hydrophobic amino acid.

Importance

Lysine is a basic amino acid, while leucine is a non-polar amino acid.

Side Chain

The side chain of lysine is a lysyl ((CH₂)₄NH₂) group, while the side chain of leucine is an isobutyl group.

Codons

The codons encoding lysine are AAA and AAG, while the codons encoding leucine are UUA, UUG, CUU, CUC, CUA, and CUG.

Conclusion                                                     

In brief, lysine and leucine are two types of essential amino acids in the human body. Both are proteogenic amino acids, and they are exclusively ketogenic. Lysine is a basic amino acid with a lysyl side chain. It is hydrophilic. The codons that encode lysine are AAA and AAG. In comparison, leucine is a nonpolar amino acid that is hydrophobic. The side chain of leucine is an isobutyl group. The codons encoding leucine include UUA, UUG, CUU, CUC, CUA, and CUG. Therefore, the main difference between lysine and leucine is their side chains.

References:       

1. “Lysine.” Mount Sinai Health System.
2. “Leucine.” Leucine – Health Encyclopedia – University of Rochester Medical Center. 

Image Courtesy:

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