Lysine

Description

Lysine is an essential amino acid. This means it must be obtained through the diet in adequate quantities to meet the body's needs.

Lysine is required in the body for the manufacture of carnitine, which is an amino acid used for the proper metabolism of fats. Lysine incorporated into proteins is often cross-linked, such as in the body proteins collagen and elastin (the major proteins of the body).

Cross-linking of lysine to make proper collagen and elastin is dependent upon the enzyme lysyloxidase, which requires copper. Copper deficiency, therefore, can result in imperfections in collagen or elastin. Lysine has also been found to stimulate the synthesis of cholesterol in the liver. High lysine/arginine ratio diets, as found in animal protein, stimulate cholesterol synthesis, whereas lower lysine-to-arginine ratio diets do not stimulate as much cholesterol synthesis.

Lysine deficiency can interfere with carnitine synthesis and have adverse impact upon fat metabolism to energy.

Lysine supplementation is helpful in the management of herpes infections. Mechanism of the action of lysine in the treatment of herpes infections in not yet known, but appears to have some effect upon the replication of the herpes virus in infected cells. Doses range between 400 and 1,000mg.

Recommended Dietary Allowances

The RDA level of lysine has been established as 50mg per day for women and 80mg per day for men. Excessive intake of lysine can result in increased urinary spill of lysine and kidney problems; therefore, doses above 1,500mg per day should not be used. Because lysine has an effect on cholesterol synthesis in the liver, its use may slightly elevate LDL cholesterol.

Food Sources

Foods high in lysine include:

Cottage cheese - dry	3,500 mg/cup
Cottage cheese - creamed	2,562 mg/cup
Fish and other seafoods	1,500-11,800 mg/lb.
Meats	2,000-8,500 mg/lb.
Poultry	4,500-6,500 mg/lb.

Method of Action

It is commonly a limiting amino acid in strict vegetarian diets in that it is in short supply in many vegetable grains. "Limiting amino acid" means its shortage in the diet may limit the synthesis of body protein and enzymes.

An unusual feature of lysine metabolism is that the alpha-amino group does not equilibrate with the nitrogen pool, as it does with most amino acids. Lysine can actually be broken down by four different pathways and is one of the more closely regulated essential amino acids in intermediary metabolism. Lysine is used along with methionine in the manufacture of carnitine, which is important for fatty acid metabolism.

Lysine is also very important for the synthesis of ribosomal proteins and its insufficiency in the diet can result in poor protein biosynthesis. By degradation of lysine to gamma-butyro betaine, it can then be converted on to carnitine. These steps require ascorbic acid (vitamin C) for their reactivity.

References

Blackburn, G.L., Grant, J.P., Young, V.R., ed. Amino Acids Metabolism and Medical Applications.

Conway, J.C., Bier, D.M., Motil, K., et al. Whole Body Lysine Flux in Young Adult Men: Effects of Reduced Total Protein and of Lysine Intake. Am. J. Physiol., 239:E192-E230, 1980.

Motil, K.J., Matthews, D.E., Bier, D.M., Burke, J.F., Munro, H.N. & Young, V.R. Whole Body Leucine and Lysine Metabolism: Response to Dietary Protein Intake in Young Men. Am J Physiol, 240:E712-E721, 1981.

Munro, H.N. & Crim, M.C. The Proteins and Amino Acids. Modern Nutrition in Health and Disease. eds. R.S. Goodhart & M.E. Shils, 6 ed., Philadelphia: Lea and Febiger, 1980.

Tews, J.K., Bradford, A.M. & Harper, A.E. Induction of Lysine Imbalance in Rats - Relationships Between Tissue Amino Acids and Diet. J. Nutr., 111:968-78, 1981.

Young, V.R., Meguid, M., Meredith, D.E. & Bier, D.M. Recent Developments in Knowledge of Human Amino Acid Requirements. Nitrogen Metabolism in Man. eds. J.C. Waterlow & J.M.L. Stephen. London: Applied Science Pubs. 1981.