The key difference between leucine and isoleucine is that the leucine synthesis involves an intermediate called alpha-ketoisovaleric acid while the isoleucine synthesis involves an intermediate called alpha-ketoglutaric acid. Also, they both differ in their functions too.
Amino acids are the building blocks of proteins. They vary based on the variable group that attaches to the chimeric carbon atom. Further, there is a total of 20 different amino acids. Among them, some are essential amino acids that we should intake via the diet. Furthermore, there are three branched-chain amino acids, which are essential. They are valine, isoleucine and leucine. Leucine and Isoleucine are isomers of each other. Both leucine and isoleucine synthesis occurs via pyruvic acid synthesis. However, the requirement of intermediates in these is different.
What is Leucine?
Leucine (short form – Leu) is an essential amino acid. It is a non – polar, uncharged amino acid. Therefore, we should include it in the diet. Meat, dairy products and soy products are rich in leucine. Leucine is a branched chain alpha – amino acid. As humans lack the enzyme required for leucine synthesis, they cannot synthesize leucine. However, plants and microorganisms can synthesize leucine from pyruvic acid since the intermediate alpha-ketoisovaleric acid is available within them.
In humans, leucine metabolism occurs in the liver, the adipose tissue and the muscle tissue. The end products of leucine metabolism are acetoacetate and acetic acid. Therefore, leucine categorizes as a ketogenic amino acid. Moreover, the functions of leucine in humans include growth and repair of muscles, production of growth hormone and regulation of energy. Also, leucine is given as a treatment for phenylketonuria.
What is Isoleucine?
Isoleucine (short form – Ile) is an isomer of leucine. It is also an essential amino acid. Therefore, human system cannot synthesize isoleucine. Hence, it is vital that the required amounts are taken via the diet. The food rich in isoleucine include eggs, meat and soy products.
Moreover, isoleucine is a branched chain amino acid synthesized in plants and microbes. Similar to leucine, isoleucine synthesis occurs during the pyruvic acid synthesis pathway. The intermediate involved is alpha-ketoglutarate. The end products of isoleucine metabolism in humans produce both Succinyl-CoA and oxaloacetate. Therefore, it belongs to both ketogenic and glucogenic groups.
Isoleucine has many functions in the human system. They include assisting wound healing process, detoxification of nitrogenous waste, stimulation of immune functions and regulating of the secretion of some hormones, etc.
What are the Similarities Between Leucine and Isoleucine?
- Leucine and Isoleucine are essential amino acids.
- Therefore, the human body cannot synthesize both the amino acids.
- However, the plants and microbes can synthesize both.
- Moreover, they both contain branched chain amino acids.
- Also, both are non – polar, uncharged amino acids.
- Leucine and Isoleucine can be obtained by meat, dairy products and eggs.
- Pyruvic acid synthesis pathway results in both these amino acids.
What is the Difference Between Leucine and Isoleucine?
Leucine and isoleucine are two branched-chain essential amino acids. Importantly, lsoleucine is an isomer of leucine. They synthesize via pyruvic acid synthesis. The key difference between leucine and isoleucine is the intermediate they require during the synthesis. Leucine requires alpha-ketoisovaleric acid while isoleucine requires alpha-ketoglutaric acid. Furthermore, there is also an another difference between leucine and isoleucine based on the functions they perform. The leucine involves in the growth and repair of muscle, production of growth hormone, and regulation of energy. Whereas the isoleucine involves in wound healing, detoxification of nitrogeneous waste, simulation of immune functions, and regulating the secretion of some hormones.
The below infographic summarizes the difference between leucine and isoleucine in tabular form.
Summary – Leucine vs Isoleucine
Leucine and isoleucine are essential, branched chain amino acids that should be taken from meals. Both are produced during the pyruvic acid pathway, but the key difference between leucine and isoleucine lies in the type of intermediates they require for the synthesis. Leucine requires alpha – ketoisovaleric acid whereas isoleucine requires alpha-ketoglutaric acid. Moreover, their physiological role also varies. Leucine involves in growth and repair of muscle tissue whereas isoleucine involves in wound healing processes and detoxification. This is the difference between leucine and isoleucine.
1.“Isoleucine.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine. Available here
“Leucine.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine. Available here