Methionine, as with other required and functional amino acids, is necessary for the normal growth and development of mammals. It plays many roles in the body, including participation in protein synthesis and is the initiating amino acid in the synthesis of virtually all proteins.
Methionine deficiency in the diet can impair the immune function. An increased methionine content, above the level required for optimal growth, improves the immune response through direct effects (protein synthesis and breakdown) and indirect effects involving methionine derivatives that have antioxidant properties.
by Daniel Luchini, Ph.D., Adisseo