Lysine is only absorbed by living organisms in the L-type. Free lysine easily absorbs carbon dioxide from the air, making it difficult to produce crystals. Generally, products exist in the form of lysine hydrochloride. Lysine is easily soluble in water, and compared to other amino acids, it is a type of amino acid that is easily absorbed orally. Lysine ingested into the body first enters small intestinal mucosal cells through active transport from the small intestinal lumen, and then enters the liver through the portal vein; In the liver, lysine participates in protein synthesis along with other amino acids. The breakdown metabolism of lysine also occurs in the liver, where it condenses with ketoglutaric acid to form yeast amino acids, which are then converted into L - α - aminohexanedioic acid semialdehyde, ultimately producing acetyl CoA. Unlike other amino acids, lysine does not participate in transamination and the deamination reaction is irreversible, making its breakdown metabolism unique. Lysine is a ketogenic amino acid, which can participate in the formation of D-glucose, lipids, and ultimately generate energy.