COQ5 (Coenzyme Q5 Homolog, Methyltransferase): COQ5 (Coenzyme Q5 Homolog, Methyltransferase) is an enzyme involved in the biosynthesis of coenzyme Q (CoQ), a vital molecule for mitochondrial energy production. It catalyzes a crucial methylation step in the CoQ pathway. Mutations in COQ5 can cause CoQ deficiency, impacting mitochondrial function and contributing to energy metabolism disorders.