Methionine is an organic compound that is one of the essential amino acids that make up the human body. Its molecular formula is C5H11O2NS, which has optical activity and is involved in protein synthesis.

Because it cannot be generated internally, it must be obtained externally. If methionine is lacking, it can cause protein synthesis to be hindered in the body, causing damage to the body. The excessive oxidation of membrane lipids caused by oxygen free radicals in the body is the cause of various damage to the body. Lipid peroxides can damage the primary and secondary lysosomal membranes, releasing the acidic phosphatase contained in the lysosome as a hydrolytic enzyme, and causing damage to important organelles such as cells and mitochondrial membranes. Methionine fights against these damages through various pathways.

Mainly used as a nutritional supplement. The physiological effect of L-methionine is the same as that of L-methionine, but its price is low (L-type is made from DL type), so DL-methionine is generally used. Restricted amino acids are found in plant-based foods such as oats, rye, rice, corn, wheat, peanut flour, soybeans, potatoes, spinach, etc. Add to the above foods to improve amino acid balance. The requirement varies with the intake of cystine. The requirement for adult males is 1.1g/d.

The taste of sea urchins is related to methionine, the sweetness of sea urchins is related to glycine and alanine, the bitterness is related to valine, and the freshness is related to glutamate. Therefore, these amino acids can be formulated as seasoning agents.

It is still used for amino acid infusion and comprehensive amino acid preparations.