Abstract
Vitamin K is a fat-soluble vitamin that plays an important role in blood coagulation and bone formation. Vitamin K has homologues due to differences in the side chain structure, phylloquinone (vitamin K1) (PK) having a phytyl side chain and menaquinones (MK - n, n = 1 to 14) having an isoprenoid side chain structure. The main vitamin K that we take from our daily diet is PK, and a fermented food, natto, contains MK-7 produced by Bacillus subtilis natto. However, the majority of vitamin K present in the tissues of mammals including humans is menaquinone-4 (vitamin K2) (MK-4) having a geranylgeranyl side chain. This reason is that PK or MK-n obtained in the diet is converted into MK-4 in the body. This phenomenon was revealed by stable isotope-labeled vitamin K study, and it was proved that the enzyme responsible for it was UbiA prenyltransferase domain containing protein 1 (UBIAD1). Recently, new vitamin K functions have been elucidated by studies using UBIAD1 gene-deficient mice. It is expected that the application of vitamin K will be expanded by clarifying the action of new vitamin K through vitamin K metabolism and conversion functions.
