a family of phylloquinones that contains a ring of 2-methyl-1,4-naphthoquinone and an isoprenoid side chain. members of this group of vitamin k 1 have only one double bond on the proximal isoprene unit. rich sources of vitamin k 1 include green plants, algae, and photosynthetic bacteria. vitamin k1 has antihemorrhagic and prothrombogenic activity. Widely distributed in green leaves and vegetables, esp. cabbage and spinach. Infant formula fortifier Vitamin K is a family of fat-soluble compounds with a common chemical structure, 2, methyl-1,4-napthoquinone. Phylloquinone is present in food of plant origin, such as green, leafy vegetables and certain plant oils, and is the predominant form in the diet. Bacterial and other forms of vitamin K, referred to as the menaquinones, differ in structure from phylloquinone in their 3-substituted lipophilic side chain. Menaquinone-4 (MK-4), which is alkylated from menadione, is present in animal feeds or is the product of tissue-specific conversion directly from dietary phylloquinone. Vitamin K is a cofactor specific to the formation of gamma-carboxyglutamyl (Gla) residues in certain proteins, including prothrombin necessary for normal hemostatic function. The naturally occurring forms of vitamin K are quinones (i.e. phylloquinone and menaquinones) so vitamin K is reduced to the vitamin K hydroquinone prior to catalyzing the gamma-carboxylation reaction. The active site for the carboxylation reaction is on the napthoquinone ring, which is identical for all forms of vitamin K, including phylloquinone and MK-4. (PMID 16857056) [HMDB]