The Substitution Of Leucine With Cysteine

AminoAcidProducts | October 23, 2020 | Amino Acids

In this article, we will have certain ideas regarding amino acid replacement and if the amino acid leucine substitution for another amino acid called cysteine is possible. Know if both of them are suitable to be replaced based on their characteristics.


Amino acids, always referred to as the building block of protein, are vital body components by the body to use them for many different body functions. Although almost all people have no issues regarding amino acids, especially the nonessential ones that the body automatically makes, and we all can get the necessary and essential amino acids from our daily diets; there are still some people who tend to have problems in having enough of the required amount of these amino acids. How does this happen? These people are suffering from amino acid deficiency wherein the body is not capable of producing enough of the nonessential amino acids or the individual’s body is unable to absorb the essential amino acids from the food they eat. If someone has an amino acid deficiency, are there ways to make sure the many can still keep up with all that has been lost?

Fortunately, most amino acids are now made into supplements which makes it easier for them to be consumed. This is also helpful for people who are not allowed to eat specific kinds of food because they have a certain health condition, but those foods are the richest source of the amino acid so they must get them from another source instead. Also, did you know that the body is capable of doing something incredible like allowing the substitution of substances when there is a lack of the other one? The same procedure applies to amino acids and it is called amino acid replacement. However, this amino acid replacement is indeed possible and helpful, but it has its restrictions that must be applied, or else the sudden mutation of two unwanted amino acids will lead to further complications such as the occurrence of rare diseases.

Amino Acid Replacement

Replacement and substitution that happens to the body may not be limited to amino acids only, but it is a huge help when the procedure is specifically done for the deficit of important amino acid. This special process in the body is one hundred percent tried and tested, but it is only required for special cases and when an amino acid is to replace another, they should both be perfect fits for each other.

The term for the safe amino acid substitution is referred to as a conservative replacement. This is the process that occurs in the body wherein one amino acid takes place of the absence of another amino acid, but this is only acceptable when the two amino acids have at least one (better if more) similarity in their properties. Although they do not happen to all people, since they are only allowed by the body if there are special cases like deficiency, it is known to be completely safe and it does not result in any form of complications or dysfunction afterward.

When talking about amino acid replacement, it is also important to know that rare cases of unwanted substitution also occur within the body – they are called radical replacement. As rare as it may be, possibilities of radical replacement happening are still out there, and there is a specific condition that results in this process which is considered to be one of the most common radical replacement to ever happen which can affect the blood and it is called the sickle cell anemia.


Out of all the twenty amino acids in the body, three of them are categorized into branch-chained amino acids or BCAAs due to their similarities in their physical traits, and sometimes it can also be because of their almost similar functions in the body. Leucine is one of the three BCAAs, together with the other amino acids isoleucine and valine.

The main function of leucine in the body is that it provides the needs of the muscles when it comes to their growth and development. This is also the reason why leucine is a common amino acid supplement that is mostly consumed by weightlifters, professional athletes, or those people who just want to flex some more muscles. Additionally, since leucine is made into a supplement, it is also because it is an essential amino acid and the consumption of leucine becomes easier when it is in supplement form. By being made into supplements, supplying the body with the desired amount of leucine is now more effortless, and it does not require the consumption of some foods most of the time.


Based on the characteristics and properties of the previously mentioned amino acid that is leucine, it may be clear how completely different it is when compared to the amino acid cysteine. Cysteine, or in more scientific terms L-cysteine, is used by the body to produce another important substance which is known as the mother of all antioxidants – glutathione.

Normally, the body can make glutathione regularly, but sometimes they tend to be overused and even some of them get depleted due to some possible conditions in the body; and this is where the L-cysteine becomes handy especially its supplement form which is better known as the N-acetylcysteine or NAC. Having enough glutathione levels in the body is very helpful in functions like the improvement of respiratory health and brain health, and also it aids the liver in terms of its detoxifying process and ridding the body of oxidative stress.

The Substitution Of Leucine With Cysteine

Leucine Substitution For Cysteine

The substitution of two amino acids may be considered as a sensitive matter, because first and foremost, whatever the result of the supposed replacement will be, it will surely make a huge impact on the body. And to be able to achieve a successful substitution, which is known as a conservative replacement, the included amino acids must have one of more common ground or similarities.

Here are the biochemical properties of amino acids that must be taken into consideration for them to result in the safe conservative replacement:

  • Charge (positive, negative, or neutral)
  • Hydrophobicity (a molecule’s reaction to water)
  • Size (molecular mass)
  • Class (e.g. aliphatic, basic, cyclic, and the like)

Most of the time, the characteristic of amino acids that are considered to be the main basis for the conservative replacement to occur is their class. For example, amino acids that are considered to be in the class of being basic which are histidine, lysine, and arginine are more likely to be acceptable combinations for a safe substitution. But in the case of leucine and cysteine?

Leucine is a known aliphatic amino acid while cysteine is a hydroxyl or a well-known amino acid containing sulfur or selenium. As far as scientific studies are concerned, it may be concluded that leucine is not a suitable substitute for cysteine. The ideal co-substitute of leucine must be the other amino acids that are aliphatic such as the two other BCAAs, glycine, and alanine. Or when it comes to an almost complete similarity it may be used as a replacement for isoleucine since they are both branch-chained, aliphatic, and characterized as hydrophobes.


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