VITAMIN K

any of several fat-soluble naphthoquinone compounds present in the leaves of plants. Vitamin K is required for the bodily synthesis of four of the blood's coagulation factors: prothrombin and factors VII, IX, and X. A deficiency of vitamin K in the body leads to an increase in clotting time of the blood (see vitamin K deficiency). In 1929 a previously unrecognized fat-soluble substance present in green leafy vegetables was found to be required for coagulation of the blood to take place. The substance was called vitamin K for Koagulation vitamin. A pure form of the vitamin was isolated and analyzed structurally in 1939; several related compounds having vitamin K activity have also been isolated and synthesized. Vitamin K1, the compound recognized in 1939, is synthesized by plants, whereas vitamin K2 is of microbial origin and is the important form in mammalian tissue. All other forms of vitamin K are converted to vitamin K2 in the body. There are a number of closely related compounds of the vitamin K2 series. Besides the natural compounds, many synthetic compounds having vitamin K activity are used to decrease blood-clotting time.