Vitamin K₂ is a mitochondrial electron carrier that rescues pink1 deficiency

Human UBIAD1 localizes to mitochondria and converts vitamin K₁ to vitamin K₂. Vitamin K₂ is best known as a cofactor in blood coagulation, but in bacteria it is a membrane-bound electron carrier. Whether vitamin K₂ exerts a similar carrier function in eukaryotic cells is unknown. We identified Drosophila UBIAD1/Heix as a modifier of pink1, a gene mutated in Parkinson's disease that affects mitochondrial function. We found that vitamin K₂ was necessary and sufficient to transfer electrons in Drosophila mitochondria. Heix mutants showed severe mitochondrial defects that were rescued by vitamin K₂, and, similar to ubiquinone, vitamin K₂ transferred electrons in Drosophila mitochondria, resulting in more efficient adenosine triphosphate (ATP) production. Thus, mitochondrial dysfunction was rescued by vitamin K₂ that serves as a mitochondrial electron carrier, helping to maintain normal ATP production.