Conversion of Menaquinone-4 in Animal Organs and its Functions

Abstract

Vitamin K is an essential factor for posttranslational modification (γ-glutamylcarboxylation) of vitamin K-dependent proteins including blood coagulation factors and bone matrix proteins. However, there are many reports regarding novel functions of vitamin K; inhibition of cell proliferation and induction of differentiation in tumor cells, and activation of nuclear receptor SXR/PXR. After ingestion from foods, vitamin K is converted to menaquinone-4, one of vitamin K2, which has geranylgeranyl moiety at 3 position of 2-methylnaphthoquinone, in various organs in human and rodent. UbiA prenyltransferase domain containing 1, UBIAD1, was identified as one of crucial enzyme for this conversion, but entire conversion process has still not elucidated completely. In this review, we described recent knowledge of menaquinone-4 conversion, novel functions of vitamin K, specially menaquinone-4, and discussed physiological meaning of menaquinone-4 conversion in tissues.