Synthesis and development of biologically active fluorescent-labeled vitamin K analogues and monitoring of their subcellular distribution

[Biological significance and metabolic activation of vitamin K]

Natural vitamin K is found in two forms: a plant form, phylloquinone (PK) and bacterial forms, menaquinones (MKs). PK is a major form of dietary vitamin K; however, the most prevalent form of vitamin K in animals and humans is menaquinone-4 (MK-4). Despite its high concentrations, the origin of MK-4 is yet to be defined. It is postulated that PK is converted into MK-4 and accumulates in extrahepatic tissues. The molecular mechanisms for these conversion reactions have been unclear. To identify the MK-4 biosynthetic enzyme, we screened the human genome database for prenylation enzyme. We found UbiA prenyltransferase domain containing 1 (UBIAD1), a human homologue of Escherichia coli prenyltransferase menA. The short interfering RNA against the UBIAD1 gene inhibited the conversion of deuterium-labelled vitamin K derivatives into deuterium-labelled-MK-4 (MK-4-d7) in human cells. We confirmed that the UBIAD1 gene encodes an MK-4 biosynthetic enzyme through its expression and conversion of deuterium-labelled vitamin K derivatives into MK-4-d7 in insect cells infected with UBIAD1 baculovirus. UBIAD1 was localized in endoplasmic reticulum. Our results show that UBIAD1 is a human MK-4 biosynthetic enzyme. This identification will permit more effective decisions to be made about vitamin K intake and bone health.

Vitamin K2 in electron transport system: are enzymes involved in vitamin K2 biosynthesis promising drug targets?

Aerobic and anaerobic respiratory systems allow cells to transport the electrons to terminal electron acceptors. The quinone (ubiquinone or menaquinone) pool is central to the electron transport chain. In the majority of gram-positive bacteria, vitamin K2 (menaquinone) is the sole quinone in the electron transport chain, and thus, the bacterial enzymes catalyzing the synthesis of menaquinone are potential targets for the development of novel antibacterial drugs. This manuscript reviews the role of vitamin K in bacteria and humans, and especially emphasizes on recent aspects of menaquinones in bacterial electron transport chain and on discoveries of inhibitor molecules targeting bacterial electron transport systems for new antibacterial agents.