| [ Summary ] |
Vitamin K occurs naturally in several forms, including the plant form, phylloquinone（PK）, and the bacterial form, known as menaquinones（MKs）. In many species, including humans, PK is a minor constituent of hepatic vitamin K content, with most hepatic vitamin K content comprising long‒chain MKs. Menaquinone‒4 (MK‒4) is ubiquitously present in a variety of tissues. It has consistently been shown that PK is endogenously converted to MK‒4. Previously, we provided evidence for the conversion of PK and K3 into MK‒4 in mouse cerebra. We verified that one human MK‒4 biosynthetic enzyme is UbiA prenyltransferase containing 1 (UBIAD1), which is a human homologue of Escherichia coli prenyltransferase menA. |