Vitamin K is a family of fat-soluble compounds with a shared quinone framework. It includes phylloquinone, conventionally called vitaminK1, and menaquinones, grouped as vitaminK2. The family supports an enzymatic modification required for several biologically active proteins, including proteins involved in coagulation.[ref]
Vitamin K Fact Sheet for Health Professionals by the Office of Dietary Supplements. Introduction: compound family and biochemical role
An important role is supporting conversion of selected glutamate residues in proteins into gamma-carboxyglutamate residues. The protein sequence and the completed chemical modification are different kinds of information. Producing a polypeptide of the expected length does not establish that all its required modifications have occurred.[ref]
Vitamin K Fact Sheet for Health Professionals by the Office of Dietary Supplements. Introduction: vitamin-K-dependent carboxylase and prothrombin
The chemistry became concrete in a 1974 prothrombin study: researchers isolated a peptide from its calcium-binding region and used nuclear magnetic resonance and mass spectrometry to identify modified glutamic acid. This linked vitamin dependence to a molecular structure that could be measured.[ref]
Vitamin K dependent modifications of glutamic acid residues in prothrombin by J. Stenflo and others. Abstract: isolated peptide and gamma-carboxyglutamic-acid identification
For a mechanistic example, consider two preparations containing the same amount of a vitamin-K-dependent protein. If one is insufficiently modified, equal protein abundance need not mean equal activity in an assay requiring the completed binding region. The example distinguishes nutrient-supported chemical maturation from simply supplying more structural protein. VitaminK is involved in several physiological systems; the name should not be reduced to a synonym for a single clotting factor.
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