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Vitamin K Biochemistry

By Dr Ananya Mandal, MD

Vitamin K is a group of fat-soluble vitamins required for the synthesis of proteins needed for blood coagulation and for the proteins required for calcium binding in bones and other tissues.

Chemically, vitamin K family members are made up of 2-methyl-1 derivatives. Two natural forms of  this vitamin exist: vitamin K1 and vitamin K2. Vitamin K1 is also called phylloquinone, phytomenadione or phytonadione and is synthesized in plants, particularly green, leafy vegetables because it is involved in photosynthesis. Vitamin K2, which is the main form stored in animals, has a number of subtypes referred to as menaquinones, homologues of the vitamin that are characterized by the different lengths of their isoprenoid side chains. There are also three synthetic forms of vitamin K – vitamins K3, K4, and K5, which have various different uses. Vitamin K3, for example is used in the pet food industry and vitamin K5 is used to inhibit the growth of fungi.

Discovery of vitamin K

In 1929, a Danish scientist called Henrik Dam looked at the role of cholesterol in the body by examining chickens that were fed a diet low in cholesterol. He found that after several weeks, the chickens tended to develop hemorrhages and start bleeding. However, restoring purified cholesterol to the diet did not rectify the defect and Dam hypothesised that another compound had been extracted from the food along with the cholesterol. That compound was the coagulation vitamin, which was described as vitamin K because the discovery was first reported in a German journal, where it was referred to as “Koagulations vitamin.”

Another scientist called Edward Adelbert Doisy of Saint Louis University carried out a lot of the research that elucidated the chemical structure and nature of vitamin K and in 1943, Dam and Doisy both received the Nobel Prize for medicine in 1943 for their findings.

In 1938, the first successful case of a jaundice patient with a prothrombin deficiency being treated with vitamin K was reported by Emory Warner, Kenneth Brinkhous, and Harry Pratt Smith from the University of Iowa.

It was not until 1974 that the exact function of Vitamin K in the body was discovered. Scientists across three laboratories isolated prothrombin, a vitamin K-dependent coagulation factor, from cows that had been given a high dose of the vitamin K inhibitor warfarin. Among the cows that were treated with warfarin, the prothrombin had ten glutamate (Glu) residues at the amino terminus, while the untreated cows had ten unusual residues that were identified as gamma-carboxyglutamate (Gla). This addition of a carboxyl group to the glutamate showed that vitamin K plays a role in converting Glu to Gla.

Reviewed by , BSc

Further Reading

Last Updated: Nov 17, 2014

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