Identification of UBIAD1 as a novel human menaquinone-4 biosynthetic enzyme

Vitamin K, an important factor in blood clotting and bone metabolism, is present in the diet principally as phylloquinone (PK) from plants. One form of the vitamin, menaquinone-4 or MK-4, has a highly specific tissue distribution in the brain, kidney and pancreas in humans and in rats, suggestive of local synthesis from phylloquinone. An enzyme catalysing that synthesis has now been identified: UbiA prenyltransferase containing 1 (UBIAD1) is a human homologue of an Escherichia coli enzyme. Previously its function was unclear, although it is a candidate gene in Schnyder crystalline corneal dystrophy. The discovery of a human MK-4 enzyme able to biosynthesize the hormonally active form of vitamin K is of relevance to work on human vitamin K requirements and bone health.