Discovery
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In the late 1920's the Danish scientist Henrik Dam investigated the role of cholesterol by feeding chickens with a cholesterol-depleted diet. After several weeks the animals developed hemorrhages and started bleeding. These defects could not be restored by adding purified cholesterol to the diet. It appeared that - together with the cholesterol - a second compound had been extracted from the food, and this compound was called the coagulation vitamin. The new vitamin received the letter K because the initial discoveries were reported in a German journal, in which it was designated as Koagulations Vitamin.
>For several decades the vitamin K-deficient chick
model was the only method of quantifying vitamin K in various foods:
the chicks were made vitamin K-deficient and subsequently fed with
known amounts of vitamin K-containing food. The extent to which
blood coagulation was restored by the diet was taken as a measure
for its vitamin K content.
It was shown that normal prothrombin contained 10 unusual amino acid residues which were identified as -carboxyglutamate (abbreviation: Gla). Prothrombin isolated from warfarin-treated cows had normal glutamate at the Gla-positions, and was designated as descarboxyprothrombin. The extra carboxyl group in Gla made clear that vitamin K plays a role in a carboxylation reaction during which Glu is converted into Gla (see structures).
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