It is generally accepted that availability of vitamin K in vivo depends on the homologues and their biological activities would be different from organ to organ. To evaluate this hypothesis, we examined the uptake, metabolism and utilization of menaquinone-4 (MK-4) and phylloquinone (PK) using their 18O-labeled compounds in two kinds of human cultured cell lines (Hep G2 and MG-63). The 18O-labeled vitamin K analogues were synthesized from naphthoquinone derivative and isoprenol. The detection of the vitamin K analogues (18O-, 16O-quinone and epoxide forms) was carried out with LC-APCI-MS/MS method. In this method, the molecular oxygen of 18O-labeled vitamin K was exchanged by atmospheric 16O2 during the formation of vitamin K epoxide with carboxylative catalytic reaction. As the results, significant difference was observed between MK-4 and PK in the amounts uptaken into the cells.
