What is Vitamin K2?
In 1929, the Danish Nutritional scientist Dr. Henrik Dam discovered that feeding chicks a totally fat-free diet caused uncontrolled bleeding under their skin¹. Dr. Dam quickly discovered the reason for this disturbing effect: the diet was missing a previously unknown fat-soluble nutrient, which he appropriately named “koagulationsvitamin” – literally, the “clotting vitamin”. The English name for the new vitamin was taken from Dr. Dam’s Danish: “K”, for “Koagulation”.
Carboxylation: Science was established that the gamma-glutamyl carboxylase is an integral cellular glycoprotein that uses vitamin K, a cofactor, to modify clusters of glutamyl residues (glu’s) to γ-carboxylated glutamyl residues (gla’s) post-translationally in vitamin K-dependent (VKD) proteins as they pass through the endoplasmic reticulum. Carboxylation is required for VKD protein functions in hemostasis. The VKD proteins, in the coagulation cascade, needing vitamin K to transact from the Glu status to Gla, to be biologically active, were proteins II, VII, IX, X, C, S and Z. It is interesting to note the surprising fact that the carboxylase itself has been shown to be a VKD protein²
For over fifty years, nearly everyone thought that the vitamin K story began and ended with blood clotting. If doctors paid attention to it at all, it was only to make sure that it didn’t interfere with the blood-thinning, anticoagulant drug warfarin (CoumadinR). But even as nutrition textbooks and mainstream medicine continued to think of vitamin K as a one-act show, a paradigm shift had been forced onto researchers in the late 1970’s when new vitamin K-dependent protein associated with bone – building osteoblast cells was discovered³ ⁴. Lian et al⁴ named it osteocalcin.
Vitamin K Analogues – Vitamin K is, in fact, a family of structurally similar, fat-soluble, 2-methyl-1,4-naphthoquinones, includ¬ing phylloquinone (K1), menaquinones (K2), and menadione (K3). The structural difference is in the substituent side chain at the gamma position.
The best-known member of the vitamin K family is phylloquinone (K1), also known as phytonadione because of its relationship with photosynthesis. Phylloquinone is found in higher plants and algae, with the highest concentrations found in green leafy vegetables⁵. Vitamin K1.derived from the food intake is selectively distributed in hepatic and non-hepatic tissues.
Menaquinones (K2) also occur naturally, but are produced by an array of bacteria, generally not by higher plants, except for K2-4. Recent studies have determined menaquinones are produced in limited quantities by animals, and by humans, from the conversion of other forms of vitamin K⁶ ⁷. The most common form of vitamin K2 in animals is menaquinone 4 (menatetrenone; MK-4), produced by the processing of exogenous and bacterial naphthoquinones⁸. Vitamins K1 and K2 differ only in the side chain in gamma position. Vitamin K1 possesses a phytyl group (partially saturated polyisoprenoid group) at position 3, while vitamin K2 possesses a repeating, unsaturated trans-poly-isoprenyl group.
- Dam H: The antihemorrhagic vitamin of the chick: occurrence and chemical nature. Nature 1935, 135:652-653.
- Berkner KL, Pudota BN: Vitamin K-dependent carboxylation of the carboxylase. Proc Natl Acad Sci U S A 1998, 95(2):466-471.
- Stenflo J: A new vitamin K-dependent protein. Purification from bovine plasma and preliminary characterization. J Biol Chem 1976, 251(2):355-363.
- Lian JB, Hauschka PV, Gallop PM: Properties and biosynthesis of a vitamin K-dependent calcium binding protein in bone. Fed Proc 1978, 37(12):2615-2620.
- Thomson RH: Naturally Occurring Quinones. New York, N.Y.: Academic Press; 1971.
- Davidson RT, Foley AL, Engelke JA, Suttie JW: Conversion of dietary phylloquinone to tissue menaquinone-4 in rats is not dependent on gut bacteria. J Nutr 1998, 128(2):220-223.
- Thijssen HH, Drittij-Reijnders MJ: Vitamin K status in human tissues: tissue-specific accumulation of phylloquinone and menaquinone-4. Br J Nutr 1996, 75(1):121-127.
- Seegers WH, Bang NU: Blood Clotting Enzymology. New York, NY: Academic Press; 1967.