Vitamin K Substances

Vitamin K comprises a group of substances, which are widespread in nature and are an essential co-factor in humans in the synthesis of several proteins that play a role in haemostasis and others that may be important in calcium homeostasis. The K vitamins all contain the 2-methyl-1,4-naphthoquinone (menadione) moiety, and the various naturally occurring forms differ in the alkyl substituent at the 3-position. Phylloquinone (vitamin K1) is 2-methyl-3-phytyl-1,4-naphthoquinone and is widely found in higher plants, including green leafy vegetables, and in green and blue algae. The menaquinones (formerly vitamin K2) have polyisoprenyl substituents at the 3-position and are produced by bacteria. The compound menadione (formerly vitamin K3) lacks an alkyl group at the 3-position but can be alkylated in vivo in some species. Several synthetic water-soluble derivatives, such as the sodium diphosphate ester of menadiol and the addition product of menadione with sodium bisulfite, also have commercial applications (National Research Council, 1989; Gennaro, 1995; Weber & Rüttimann, 1996).