Vitamin K Converting Enzyme and Its Biological Significance

Abstract

Vitamin K, a fat-soluble vitamin that plays important roles in blood coagulation and bone formation, has homologues with different side chain structures. Humans mainly consume vitamin K₁ (phylloquinone, PK) in green vegetables and menaquinones (MK-n, n = 6－14) in fermented foods. However, the most abundant vitamin K in the body is vitamin K₂ (menaquinone-4, MK-4), due to the fact that ingested PK and MK-n are converted to MK-4 in the body. The enzyme responsible for this conversion reaction is UbiA prenyltransferase domain containing protein 1 (UBIAD1), and the conversion to MK-4 occurs in tissues throughout the body. This article describes the mechanism responsible for conversion of vitamin K homologues to MK-4 discovered by the author, the important role of UBIAD1, and newly clarified biological functions of vitamin K revealed by the use of UBIAD1-deficient mice.