Difference Between Lysine and Leucine

The key difference between lysine and leucine is that lysine is an aliphatic alpha amino acid, whereas leucine is a branched alpha amino acid.

Lysine and leucine are alpha amino acid molecules that are essential for our body. An alpha-amino acid is an amino acid molecule containing an amino group, a carboxylic acid group and a side chain of hydrocarbon units.

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

What is Lysine?

Lysine is an alpha amino acid molecule that is useful in protein biosynthesis. We can abbreviate this amino acid name as Lys or K. This amino acid contains an alpha amino group, an alpha carboxylic acid group, and a side chain lysyl. The lysyl chain makes this amino acid a basic compound. It also makes lysine a charged and aliphatic amino acid. The codons that encode for the lysine amino acid are AAA and AAG. The alpha carbon atom of this molecule is chiral, and it occurs as a racemic mixture of its enantiomers (L and D enantiomers).

Figure 01: The Chemical Structure of Lysine

Our body cannot synthesize lysine molecules. But it is an essential component in humans. Therefore, we must obtain it from food. However, there are some organisms that can synthesize lysine through two main biosynthetic pathways: diaminopimelate pathway and alpha aminoadipate pathway. Moreover, the catabolism of lysine occurs through the saccharopine pathway.

There are several roles of lysine in the human body, including proteinogenesis, crosslinking of collagen polypeptides, uptake of essential mineral nutrients, in the production of carnitine, etc. Moreover, it is often involved in histone modifications and impacts the epigenome.

Since it is an essential amino acid, the lack of lysine in our body can cause several diseases, including defective connective tissues, impaired fatty acid metabolism, anaemia, and systemic protein energy deficiency.

What is Leucine?

Leucine is an amino acid that is useful in the biosynthesis of proteins. We can abbreviate its name as Leu or L. It is an essential alpha amino acid because it contains an alpha amino acid group, an alpha carboxylic acid group, and a side chain isobutyl group that makes it a nonpolar aliphatic amino acid. Moreover, this is an essential amino acid in humans, and our body can’t synthesize it. Therefore, we need to take it from the diet. Meat, dairy products, soy proteins and beans mainly contain leucine. The codons that encode leucine include UUA, UUG, CUU, CUC, CUA, and CUG.

Figure 02: The Chemical Structure of Leucine

This amino acid is useful as a food additive where it has the E number E641. We can classify it as a flavor enhancer. In the forms of dietary supplement, leucine can slow down the degradation of muscle tissue by increasing the synthesis of muscle proteins in aged rats, according to some research studies. But the long-term intake of leucine has not increased muscle mass or strength in healthy elderly men.

What are the Similarities Between Lysine and Leucine?

Lysine and leucine are alpha amino acids.
Both are essential to our body.
These amino acids are not synthesized in our body; we need to take them from our diet.

What is the Difference Between Lysine and Leucine?

Lysine and leucine are alpha amino acid molecules that are essential to our body. The key difference between lysine and leucine is that lysine is an aliphatic alpha amino acid whereas leucine is a branched alpha amino acid.

The following table summarizes the difference between lysine and leucine.

Summary – Lysine vs Leucine

Lysine and leucine are alpha amino acid molecules that are essential to our body. In other words, these amino acids contain a similar basic chemical structure of a central carbon atom consisting of an amine group, a carboxylic acid group and a side chain of hydrocarbon units attached to the central carbon. The key difference between lysine and leucine is that lysine is an aliphatic alpha amino acid, whereas leucine is a branched alpha amino acid.

Reference:

1. “Leucine.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine.

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