Only l-lysine is absorbed by the organism. Free lysine readily absorbs carbon dioxide from the air, making it difficult to crystallize, and generally available in the form of lysine hydrochloride. Lysine is soluble in water and, compared to other amino acids, is the most easily absorbed by oral administration. Lysine intake in the body is first transported by active transport into small intestinal mucosa cells, and then into the liver through the portal vein. In the liver, lysine is involved in protein synthesis along with other amino acids. Lysine catabolism also occurs in the liver, where it condenses with ketoglutaric acid to form yeast amino acids, which are converted to L-α -aminoadipate hemaldehydes and eventually to acetyl coA. Unlike other amino acids, lysine does not participate in transamination and the deamination reaction is irreversible, so lysine catabolism is very special. Lysine is a ketogenic amino acid and therefore can be involved in the formation of D-glucose, lipids, and ultimately energy.

Lysine is involved in carnitine biosynthesis in vivo. Carnitine plays an important role in fat metabolism and is an essential cofactor in fat metabolism. Lysine is one of the precursors of carnitine synthesis, so lysine supplementation can speed up fat metabolism in the body. Lysine has a strong function through the blood-brain barrier, can directly enter the brain tissue, affect the respiratory chain, for nerve cell repair and normal physiological activities to provide the necessary energy source.

Lysine can chelate with calcium, iron and other mineral elements to form soluble small molecular monomers to promote the absorption of these mineral elements.

Lysine is considered as a non-specific bridging molecule, which can bind antigen to T cells and cause T cells to produce specific effects on antigen.

Lysine, as an essential amino acid, is involved in the synthesis of skeletal muscle, enzymes, serum proteins, polypeptide hormones and other proteins.

The chemical name for Lysine is 2, 6-diaminocaproic acid. Lysine is a basic essential amino acid. Because the lysine content in cereal food is very low, and is easy to be destroyed in the process of processing and lack, it is called the first limiting amino acid.

Lysine is one of the essential amino acids of human beings and mammals, which cannot be synthesized by the body itself and must be supplemented from food. Lysine is found mainly in animal foods and legumes, and is very low in cereals. Lysine has positive nutritional significance in promoting human growth and development, enhancing body immunity, antiviral, promoting fat oxidation, relieving anxiety and other aspects, but also can promote the absorption of some nutrients, can work synergistically with some nutrients, and better play the physiological functions of various nutrients.

The active component content of L-lysine is generally 77% to 79%. Monogastric animals are completely unable to synthesize lysine by themselves and do not participate in transamination. Only after the amino of D-amino acids and L-amino acids are acetylated can they be deaminated by d-amino acid oxidase or L-amino acid oxidase. After deamination, the ketoacid will not be aminated, that is, the deamination reaction is irreversible. Therefore, it is often insufficient in animal nutrition.

The absorption efficiency of D-lysine is different from that of L-lysine. D-lysine can hardly be absorbed and utilized, while L-lysine is the main bioactive one. The ε -amino of lysine is very active, and it is easy to combine with the active carbonyl group in feed and form complex which is difficult to be absorbed and utilized.