Vitamin K is essential for several physiological processes, such as blood coagulation, in which it serves as a cofactor for the conversion of peptide-bound glutamate to γ-carboxyglutamate in vitamin K-dependent proteins. This process is driven by the vitamin K cycle facilitated by γ-carboxyglutamyl carboxylase, vitamin K epoxide reductase and ferroptosis suppressor protein-1, the latter of which was recently identified as the long-sought-after warfarin-resistant vitamin K reductase. In addition, vitamin K has carboxylation-independent functions. Akin to ubiquinone, vitamin K acts as an electron carrier for ATP production in some organisms and prevents ferroptosis, a type of cell death hallmarked by lipid peroxidation. In this Perspective, we provide an overview of the diverse functions of vitamin K in physiology and metabolism and, at the same time, offer a perspective on its role in ferroptosis together with ferroptosis suppressor protein-1. A comparison between vitamin K and ubiquinone, from an evolutionary perspective, may offer further insights into the manifold roles of vitamin K in biology.
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