Methionine: Benefits, Side Effects, Dosage, and Interactions

Chapter: Amino Acids

AKA: L-methionine.

A sulfur-containing amino acid.

Food Sources: Found only in animal foods such as eggs, fish (all kinds), liver, meat (all kinds), milk, and poultry (all kinds).

Effects: Methionin is an antioxidant that is also said to protect against the accumulation of chemicals and heavy metals (e.g., cadmium, mercury) in the brain and body, play a key part in the production of the brain neurotransmitter choline (not to mention adrenaline, lecithin, and vitamin B12), prevent fat from getting into the arteries and liver, render selenium available to the body, and play an important role in the biosynthesis of two other amino acids - cysteine and taurine. Methionine is believed to relieve some cases of schizophrenia by lowering the level of histamine in the blood, and has been useful in the treatment of arthritis, cataracts, high cholesterol, chronic pain, asthma, allergies, and some cases of Parkinson's disease. It may help protect the liver against damage from carbon tetrachloride, and prevent certain tumors when used in combination with choline and folic acid.

Deficiency symptoms include bad skin tone, loss of hair, a buildup of toxic wastes in the body and fat in the liver, anemia, impeded protein synthesis, and atherosclerosis.

Selenomethionine is a variant in which selenium atoms replace the sulfur atoms.

Precautions: Methionine should always be taken with B-6 -to prevent an excess of homocysteine - and magnesium. Capsules are preferable to other forms because they avoid the rotten egg smell that usually accompanies it.

One study suggests that methionine might be destroyed by excessive alcohol consumption.

Dosage: 100 to 250 mg/day. Leon Chaitow, N.D., D.O., recommends 200 to 1000 mg/ day with vitamin B-6 and magnesium; Sheldon Saul Hendler, M.D., Ph.D., advises against supplementation.

Questions and Answers

What would the difference be if the cysteine amino acids were replaced by methionine ?, I had to draw a chemical structure-I do know that the cysteine amino acid is a polar neutral acid and that the methionine is a nonpolar one but what is the difference otherwise?? Thanks!

wiki has a page on each if you google them.

Methione is only slightly soluble in water (non-polar) to about 4g/100g whereas cysteine is extremely soluble. Thus solubility would decrease.

Does that help?

Why is methionine the first amino acid in every growing polypeptide?, And say that methionine was not the first amino acid in the chain, what would be the consequences?
Thanks in advance :)

The AUG/methioinine is important in that it carries the "Start" message for a ribosome that signals the initiation of protein translation from mRNA. As a consequence, methionine is incorporated into the N-terminal position of all proteins in eukaryotes and archaea during translation, although it is usually removed by post-translational modification.
So basically without that .... there want b an ainitiation of translation/protein synthesis.

Thereare also viruses who are cunning and wants to incorporatethemselve into our genetic mechanism that uses multiple AUG start site to initiate different types of viral protein sequences. So basically the methionine incorporation is universal.

Why is methionine the start codon?, Methionine only has one codon that codes for it, but so does tryptophan. So why is methionine the start codon and not another amino acid?

Translation starts with a chain initiation codon (start codon). Unlike stop codons, the codon alone is not sufficient to begin the process. Nearby sequences and initiation factors are also required to start translation. The most common start codon is AUG which is specifically recognised by the other factors necessary.

Where can I buy methionine in central London?, I've been doing some research lately and am almost certain that I suffer from histadelia and would like to try and treat it with methionine. The only problem is I don't have a clue where to get it from. If anybody else uses it or knows where to get it from could you please tell me.

Thanks

p.s. I don't want to buy online.

I would suggest you try health food shops, they sell it as a body building supplement.

How do we determine the starting methionine in a polypeptide?, From what I've learned from my first few college lectures, all proteins (or at least most of them, I think; correct me if I'm wrong) start with the amino acid methionine. My question is, when characterizing a certain polypeptide, how can we tell which methionine is the starting amino acid for that polypeptide chain, if the polypeptide contains more than one methionine?

If you're looking at the polypeptide, then the first one is the first one.

If you're looking at the mRNA, then the first AUG codes for the first methionine.

If you're looking at the DNA, then it's the first TAC that is coded for and not removed as an intron.

However, not all polypeptides end up beginning with methionine. In most, the initial methionine is removed during processing in the ER.

would it be safe to feed a draft cross 1300mg of l-lysine and 1800mg of dl-methionine?, he has horrible feet and these are supposed to promote hoof growth. im not 100% how much to give him. i haven't found anything that says too much can be toxic and these numbers are in the ranges of recommended doses. any help would be greatly appreciated.

L-Lysine I'd give him anything between 500mg - 1500mg

Not such about the dl-methionine though...

I'm guessing he's big? so he should be able to hack it!
Us humans can take 1500mg a day of L-Lysine so he should be fine with more... (to stop cold-sores)

what experiment was performed that led to the find that AUG (methionine) is the initiation codon?, i want to know the first experiments that were performed in support of the fact that AUG (methionine) is the start codon

From what I understand, the way they figured out which codon coded for each peptide was essentially this:

- Create an mRNA chain (i.e.: AAAAAAAAAAAA)
- Introduce the mRNA to a test tube including ribosomes and only one peptide at a time, as well as other materials to encourage protein synthesis.
- Check to see which test tube created protein / polypeptides. The peptide added to that test tube is what your mRNA coded for.

All my instructor said about the mixed codons (AUG included) was that the experiment was more involved, but similarly set up.

All proteins begin with the amino acid methionine which is the start codon.?, True or False?

False, AUG is the start codon coding for methionine but the methionine may be cleave off during post-translational processing before you have a functional protein.

Why methionine is the starting amino acid in protein synthesis?, I want to know why only methionine initiates protein synthesisout of 20 naturally available amino acids. Also, i would like to know what codons code for methionine other than AUG.

DNA is just a continuous sequence of bases (ATCG) that gets transcribed to RNA (AUCG). The machinery that translates the RNA to protein (the ribosome) must know where to start reading the message. That's why the start codon is AUG and it just happens to code for a methionine amino acid. No other reason that I know of than that. The ribosome just knows to start at AUG.

Why do onions release such a potent odor, though they contain very little methionine or cysteine?, ...in comparison to other foods.

Sulfur is your culprit.

Continue reading here: Metoclopramide Risk Summary

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