Methionine

About Methionine

Methionine is an essential sulfur containing amino acid. It holds a special place in protein synthesis because the start codon used to initiate translation encodes methionine, so it is the first amino acid of most newly made proteins, although it is often removed afterward. Methionine is converted to S adenosylmethionine, the main methyl donor used in methylation of DNA, proteins, neurotransmitters and phospholipids. After donating its methyl group it becomes homocysteine, which can be recycled back to methionine with the help of folate, vitamin B12 and betaine, or converted to cysteine through the transsulfuration pathway that requires vitamin B6. Elevated blood homocysteine reflects disturbances in this cycle. Methionine is abundant in eggs, fish, meat and dairy, as well as Brazil nuts and sesame, while legumes contain relatively less. Methionine restriction has been shown to extend lifespan in rodents and is an active area of aging research, though its relevance to humans is unclear.