Vitamin k

Vitamin K is a fat-soluble vitamin essential for maintaining clotting, as it is crucial for the synthesis of serine proteases of factors II, factor VII, factor IX, factor X and the proteins S, protein C and protein Z.

Vitamin K catalyzes the final step in the synthesis of the various coagulation factors. The decisive step is the y-carboxylation of the precursors. This process is part of the vitamin K cycle: vitamin K is converted into the hydroquinone form of vitamin K by an NADH reductase. This form serves as an O2 acceptor. Under the influence of a carboxylase, together with CO2 as substrate, glutamic acid is carboxylated to y-carboxyl-glutamic acid.
An epoxidase converts the hydroquinone form of vitamin K into the 2,3-vitamin K epoxide (naphtoquinone epoxide). The vitamin K epoxide regenerates the vitamin K via an epoxide reductase, which is then again available as the starting point for the vitamin K cycle. The fermentation system, consisting of carboxylase, epoxidase and epoxide reductase, is located on the inside of the membranes of the rough endoplasmic reticulum.

The starting point for the discovery of vitamin K was a chicken feed extracted with ether in 1929 by Hendrik Dam (1895-1976) and thus fat-free. The chickens became anaemic and showed a strong tendency to bleed. Similar observations were made by researchers McFarlane and Almqvist. Initially, Dam suspected that the experimental animals suffered from scurvy. However, the addition of vitamin C, other vitamins and cholesterol brought no improvement. Only the addition of hemp seed led to a healing of the animals. Dam gave the effective substance the name vitamin K, like coagulation vitamin. He found out that the cause of bleeding was a prothrombin deficiency. Later it turned out that vitamin K was also needed for the synthesis of factors II, IX, and X. At the end of the 1930s, it was observed that patients with occlusive scterus developed a prothrombin deficiency because the bile salts were responsible for the absorption of vitamin K. In 1939, the American Edward Doisy (1893-1985) succeeded in isolating vitamin K and clarifying its structure. Dam and Doisy were awarded the Nobel Prize in Medicine in 1943.

1. HA Neumann (2014) The coagulation system. ABW-Scientific Publisher GmbH Berlin