Active Forms, Antagonists, Physical Properties, and Synthesis of Vitamin K
The nomenclature of compounds possessing vitamin K activity has been modified a number of times since the discovery of the vitamin. The observation that the chlorinated form of a benzoquinone analog of vitamin K, 2-chloro-5,6-dimethyl-1,4-benzoquinone was also an antagonist of vitamin K provided further evidence of a direct action of these compounds. Data obtained by the oral administration of the vitamin to vitamin K-deficient chicks show that isoprenalogs with three to five isoprenoid groups in either a menaquinone- or a phylloquinone-type compound have maximum activity. Partial purification of the vitamin K-dependent carboxylase made it possible to study the impact of a number of analogs of phylloquinone on the carboxylase, rather than indirectly through their effect on clotting factor levels in animals. The major use of vitamin K is in poultry diets. Chicks are very sensitive to vitamin K restriction, and antibiotics that decrease intestinal vitamin synthesis are often added to poultry diets.