Coenzyme Q9 (CoQ9) is a nine isoprenyl group-containing member of the mitochondrial ubiquinone family that is thought to be necessary for the biosynthesis of CoQ10 in humans. Mutations in the gene that encodes CoQ9 are associated with encephalomyopathy and autosomal-recessive, neonatal-onset, primary CoQ10 deficiency. While in humans CoQ10 predominates, mice and C. elegans primarily rely on CoQ9 for electron transport through the mitochondrial respiratory chain and for antioxidant functions.
