抄録
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 (abbreviated as vitamin K 1, 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 (abbreviated as vitamin K 2, 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 has already been reported around 1960. However, the scientific proof that PK and MK-n are converted into MK-4 in vivo was not enough, so that the fact was not fully accepted. We scientifically proved for the first time that PK and MK-n are converted to MK-4 using stable isotope-labeled vitamin K. In 2010, we further identified that UbiA prenyltransferase domain containing protein 1 (UBIAD1) is responsible for the conversion reaction of PK and MK-n to MK-4 in vivo .
However, the physiological roles of MK-4 in all tissues of the whole body and the physiological significance of MK-4 converted from PK and MK-n by UBIAD1 have not been sufficiently elucidated yet. To investigate the function of UBIAD1 in vivo , we generated UBIAD1 systemic knockout mice and tissues-specific UBIAD1 knockout mice. In this paper, we introduce the findings of the mechanism that the transformation of MK-4 is caused by UBIAD1 and the physiological significance of this transformation which are based on our research.
