l-Lysine is one of numerous amino acids that the body needs for growth and tissue repair. It is classified as one of the nine “essential” amino acids because our bodies do not produce it. Like all amino acids, lysine is a building block for proteins. It also plays a role in the production of various enzymes, hormones, and disease-fighting antibodies. 

The richest sources of l-lysine include red meats, fish, and dairy products (milk, eggs, and cheese). Vegetables are generally a poor source of lysine, with the exception of legumes (beans, peas, and lentils). The daily recommended requirement for an adult is approximately 12 mg/kgbw, which represents approximately 800 mg. While most of the needs for lysine are met through dietary sources, supplements are now popular for treating and preventing specific ailments as well. Lysine has a net positive charge at physiological pH values, making it one of the three basic (with respect to charge) amino acids. This polar amino acid is commonly found on the surfaces of proteins and enzymes, and sometimes appears in the active site. Lysine is incorporated into proteins at the rate of 7% on a molar basis compared to other amino acids.