Difference Between Lysine and Arginine

The key difference between lysine and arginine is that lysine is a basic amino acid that is essential to humans, while arginine is a basic amino acid that is not essential to humans.

Lysine and arginine are positively charged basic amino acids. Both are hydrophilic amino acids. Generally, basic amino acids are polar. They are mostly present on protein surfaces. Their pKa values are very high, so they tend to bind with protons and gain a positive charge in the process. These two amino acids in the protein surfaces play a very important role in protein stability. They form ionic interactions and hydrogen bonds in the proteins. They also interact with water molecules.

CONTENTS

1. Overview and Key Difference
2. What is Lysine 
3. What is Arginine
4. Similarities – Lysine and Arginine
5. Lysine vs Arginine in Tabular Form
6. Summary – Lysine vs Arginine

What is Lysine?

Lysine is a positively charged basic amino acid that is essential to humans. It provides less stability to proteins due to its geometric structure. This amino acid was first discovered from protein casein in milk by German biochemist Ferdinand Heinrich Edmund Drechsel in 1889. It is an α-amino acid that involves in protein biosynthesis. It has an α-amino group, α-carboxylic acid group, and a lysyl side chain. The human body cannot synthesize lysine. Therefore, lysine is an essential amino acid. It has to be obtained from the diet. However, some organisms can produce lysine through two biosynthetic pathways called diaminopimelate and α-aminoadipate pathways. But these pathways need distinct enzymes and substrates that are not present in humans.

Lysine Benefits

Lysine plays several important roles in humans. The most important role is proteinogenesis. It helps in crosslinking of collagen polypeptides and uptake of essential minerals. Furthermore, it helps in the production of carnitine. Also, lysine is often involved in epigenetic histone modifications. Therefore, it impacts the epigenome. Due to its importance in biological processes, the lack of this amino acid can lead to several diseases such as defective connective tissues, impaired fatty acid metabolism, anaemia, and systematic protein-energy deficiency. In contrast, an overabundance of this amino acid causes neurological disorders.

What is Arginine?

Arginine is a positively charged basic amino acid that is not essential to humans. It provides more stability to a protein due to its geometric structure. This amino acid was first isolated from yellow lupin seedlings by the German scientist chemist Ernst Schulze and his assistant Ernst Steiger in 1886. It is also an α-amino acid amino acid involved in protein biosynthesis. It contains α-amino group, α-carboxylic acid group, and a side chain consisting of a 3- carbon aliphatic straight-chain ending in a guanidino group. It is the precursor for the biosynthesis of nitric oxide.

Since it can be synthesized in the human body, arginine is considered a semi-essential or non-essential amino acid. Though it is a non-essential amino acid, preterm infants are unable to synthesize arginine internally, making it nutritionally essential for preterm infants. Most healthy people do not want arginine because it is a component of all protein-containing foods. Moreover, the human body can synthesize it from glutamine via citrulline.

What are the Similarities Between Lysine and Arginine?

• Lysine and arginine are positively charged basic amino acids.
• Both have high pKa values.
• They are polar and hydrophilic amino acids.
• Both are aliphatic amino acids.
• They form ionic interactions and hydrogen bonds in the proteins.
• They are both found on protein surfaces.

What is the Difference Between Lysine and Arginine?

Lysine is an essential basic amino acid, while arginine is a non-essential basic amino acid. So, this is the key difference between lysine and arginine. Furthermore, lysine provides less stability to protein due to its geometric structure, while arginine provides more stability to protein due to its geometric structure. Thus, this is another significant difference between lysine and arginine.

The below infographic lists more differences between lysine and arginine in tabular form for side by side comparison.

Summary – Lysine vs Arginine

Lysine and arginine are two basic amino acids. Their side chain groups contain a full positive charge at the physiological pH. They form various electrostatic interactions in the proteins. Hence, these amino acids play important roles in protein stability. Lysine provides less stability to protein due to its geometric structure, but it is essential to humans. In contrast, arginine provides more stability to protein due to its geometric structure; however, it is not essential to humans. Thus, this is the summary of the difference between lysine and arginine.

Reference:

1. Sokalingam, Sriram, et al. “A Study on the Effect of Surface Lysine to Arginine Mutagenesis on Protein Stability and Structure Using Green Fluorescent Protein.” PLOS ONE, Public Library of Science.
2. “Arginine.” Encyclopædia Britannica, Encyclopædia Britannica, Inc..

Image Courtesy:

1. “Lysine w functional group highlighted” By Clavecin – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Arginine“ (CC BY-SA 3.0) via Commons Wikimedia