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Phylloquinone (Vitamin K)
Vitamin K (koagulation vitamin) is an essential nutrient required for the normal biosynthesis and activation of several key proteins. There are three forms of this vitamin.
, also known as phylloquinone or phytonadione, is found in green plants and is the form included in dietary supplements.
, also called menaquinone, is produced by bacteria, including some found in the human intestinal tract.
or menadione, a synthetic derivative, is used as a source of vitamin K in animal feeds.
Vitamin K is an essential cofactor for enzymatic activity. It assists in the enzymatic carboxylation of glutamic acid, an amino acid found in most proteins. This carboxylation occurs after the amino acid has been incorporated into the protein chain. The added carboxyl (-COOH) groups provide a site at which calcium can bind to the protein. Through the above activity, vitamin K is involved in converting an inactive precursor of prothrombin (blood coagulation factor II) into biologically active prothrombin.
Vitamin K is similarly involved in the synthesis of at least five other proteins involved in the regulation of blood clotting. In all cases, it is thought that vitamin K assists in activating these proteins through establishment of calcium binding sites. Other vitamin-K-dependent proteins whose function depends on calcium binding have been identified in bone, kidney, and vascular tissues. In bone, these proteins appear to be involved in bone crystal formation and bone remodeling. As a result, the potential role of vitamin K in osteoporosis has received increasing attention.
Food sources of vitamin K primarily include green vegetables, including spinach, broccoli, brussels sprouts, kale, and turnip greens.
There is no known toxicity associated with the administration of high doses of phylloquinone, a natural form of the vitamin.
For additional information (including a list of references), please refer to the vitamin K technical bulletin at http://www.usana.com/dotCom/company/science/components
Vitamin K - U.S. National Library of Medicine
Vitamin K - Physicians' Desktop Reference
Vitamin K - Wikipedia
Vitamin K - Linus Pauling Institute