L Methionine structure function and biological role in protein synthesis
Human beings possess an essential amino acid known as L Methionine. This compound plays a vital part in the health and metabolism of multiple species and also in human beings. Moreover, it is a crucial bit of angiogenesis (development of new blood vessels).
Methionine Structure
Between two amino acids, Methionine contains sulphur while the other one is cysteine. Generally, every amino acid holds a similar structure that is an amino group connected to one hydrogen, one side is a chain group and the other is a carboxyl group. Moreover, Methionine's chemical formula is C5H11NO2S, and its side chain is C2H7S.
Following is a diagram that shows Methionine structure
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Dietary Sources of L –Methionine
High concentrations of L-methionine are present in meat, eggs, Brazil nuts and sesame seeds. Notably, it is also available in some seeds of plants and cereals. However, maximum vegetables and fruits hold low levels of L-Methionine.
Maximum legumes have a low amount of protein content, and hence they are low in L-Methionine. Moreover, the protein sources which do not have enough of L-Methionine are not counted as complete proteins. Due to this reason, sometimes pet foods are mixed with racemic Methionine.
Furthermore, individuals must not overcook or excessively boil food products containing L – methionine. It may damage the amino acid structure as they are hugely soluble.
A Tabular Representation Showing Sources of Food Containing Methionine.
Effectiveness Of L Methionine
The most important use of Methionine is for the treatment of acetaminophen poisoning. Although there is a lack of evidence, this amino acid may also be useful for the following diseases:
Breast Cancer
Humans who intake high quantities of Methionine are less prone to breast cancer.
Parkinson's Disease
Some studies suggest that if individuals take L-methionine via food for at least six months, they may experience improvement in Parkinson's disease symptoms like tremor, rigidity and incapability of controlling movements.
Neural Tube Defects at the Time of Birth
Females who eat more amounts of L-methionine during their pregnancy may have a reduced risk of neural tube issues.
Apart from the mentioned diseases, Methionine can improve several other health conditions like herpes simplex virus (HSV), pancreatitis, asthma, schizophrenia, depression, liver function, shingles, human papillomavirus, allergies, urinary tract infections, etc.
Moreover, there are other Methionine uses as well. It can be used as an additive to dogs as it assists in lessening the growth of kidney stones in them. Also, it acts as a pesticide to fight against caterpillars (giant swallowtail) which damage orange crops.
Impact On Health
Reduction of L-methionine is related to hair greying. Due to loss of this amino acid, hydrogen peroxide gets built up in follicles of hair which results in lack of tyrosinase effect. Hence, it further leads to hair discolouration.
On the other hand, large doses of Methionine may affect the human brain and cause heart diseases. Also, it can enhance the development of a few tumours. Hence, Methionine must not be used by self-medication.
Do It Yourself
1. L – methionine is essential for growth of _________ ________ in the human body.
2. High levels of methionine is available in _________, _________, _________ and _________.
3. L – methionine is vastly used for the treatment of __________ __________.
4. The chemical formula of methionine is _________.
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FAQs on L Methionine Essential Sulfur Containing Amino Acid
1. What is L-methionine?
L-methionine is an essential sulfur-containing amino acid that the human body cannot synthesize and must obtain from the diet. It is one of the 20 standard amino acids used in protein synthesis and is encoded by the genetic code as AUG during translation. L-methionine:
- Contains a thioether (-S-) group in its side chain.
- Serves as a precursor for important molecules like S-adenosylmethionine (SAM).
- Is found in high-protein foods such as eggs, meat, fish, and legumes.
2. What is the function of L-methionine in the body?
The main function of L-methionine is to initiate protein synthesis and act as a methyl group donor through its derivative S-adenosylmethionine (SAM). Its key roles include:
- Serving as the start amino acid in mRNA translation (AUG codon).
- Participating in methylation reactions that regulate DNA, RNA, and proteins.
- Contributing to the synthesis of cysteine via the transsulfuration pathway.
3. Why is methionine called an essential amino acid?
Methionine is called an essential amino acid because the human body cannot synthesize its carbon skeleton and must obtain it from dietary sources. Unlike non-essential amino acids, humans lack the metabolic pathways to produce methionine from simpler compounds. Therefore:
- It must be consumed in food.
- Deficiency can impair protein synthesis and growth.
- It is crucial during periods of rapid development, such as childhood.
4. How does L-methionine initiate protein synthesis?
L-methionine initiates protein synthesis by binding to the start codon (AUG) on mRNA during translation. The process occurs as follows:
- The ribosome recognizes the AUG start codon.
- An initiator tRNA carrying methionine binds to this codon.
- Protein elongation then proceeds by adding other amino acids.
5. What is the structure of L-methionine?
L-methionine has a central α-carbon bonded to an amino group, carboxyl group, hydrogen atom, and a sulfur-containing side chain. Its structural features include:
- A molecular formula of C₅H₁₁NO₂S.
- A side chain containing a thioether (-CH₂-CH₂-S-CH₃) group.
- Being one of the two sulfur-containing amino acids, along with cysteine.
6. What is the difference between methionine and cysteine?
The main difference between methionine and cysteine is that methionine is an essential amino acid with a thioether group, while cysteine is a non-essential amino acid with a thiol (-SH) group. Key differences include:
- Methionine: contains a thioether and cannot form disulfide bonds.
- Cysteine: contains a thiol group and forms disulfide bonds in protein structure.
- Cysteine can be synthesized from methionine via the transsulfuration pathway.
7. What is S-adenosylmethionine (SAM) and how is it related to methionine?
S-adenosylmethionine (SAM) is a key methyl donor molecule formed from L-methionine and ATP. In cells:
- Methionine reacts with ATP to form S-adenosylmethionine.
- SAM donates methyl groups in DNA methylation and other biochemical reactions.
- After methyl donation, SAM is converted to S-adenosylhomocysteine.
8. What foods are high in L-methionine?
Foods high in L-methionine are mainly protein-rich animal and plant sources. Common examples include:
- Animal sources: eggs, fish, chicken, beef, and dairy products.
- Plant sources: sesame seeds, Brazil nuts, soybeans, and lentils.
- Cereal grains such as oats and rice.
9. What happens if there is a methionine deficiency?
A methionine deficiency can impair protein synthesis, growth, and methylation processes in the body. Potential effects include:
- Reduced synthesis of essential proteins.
- Disruption of DNA methylation and cellular regulation.
- Impaired production of cysteine and related sulfur-containing compounds.
10. Is methionine involved in detoxification processes?
Yes, methionine supports detoxification by contributing to the synthesis of glutathione through its conversion to cysteine. The pathway involves:
- Conversion of methionine to homocysteine.
- Formation of cysteine via the transsulfuration pathway.
- Use of cysteine to produce glutathione, a major cellular antioxidant.
