Methionine

A sulphur-containing amino acid, the starting point of the methylation cycle (SAM synthesis) and a precursor of cysteine, taurine and glutathione.

What methionine does in the body

Methionine is an essential, sulphur-containing amino acid; every newly formed protein chain begins with it. Using energy from ATP and magnesium, methionine is converted into S-adenosylmethionine (SAM), the body's most important methyl group donor: SAM methylates genetic material and so controls genes, and is involved in producing creatine, phosphatidylcholine for cell membranes and fat transport, adrenaline and melatonin. What remains is homocysteine. It is either converted back to methionine with folate and vitamin B12 or with betaine – closing the methylation cycle – or broken down to cysteine with vitamin B6. Cysteine gives rise to glutathione, taurine and sulphate.

Low methionine – what happens in the body?

When little methionine is available, less SAM is produced and methylation runs more slowly – in the production of creatine as well as of phosphatidylcholine, which the liver needs to pack fat into lipoproteins and release it. Less cysteine is produced via the breakdown pathway, so less starting material is available for glutathione and taurine too. Low values occur with low protein intake, malnutrition and a diet in which pulses are the main protein source, because they contain little methionine.

High methionine – what happens in the body?

Methionine is processed mainly in the liver; when liver function is impaired, the value in the blood rises. A lot of methionine leads to more homocysteine, especially when folate, vitamin B12 or vitamin B6 are scarce and homocysteine is neither converted back nor broken down. In inherited homocystinuria, in which breakdown to cysteine is blocked, methionine and homocysteine accumulate together; a rare inherited bottleneck in SAM production raises methionine alone. After protein-rich meals the value rises temporarily.

The interpretation is given in your report.