Coenzyme Q4, often abbreviated as CoQ4, is a member of the ubiquinone family, a group of lipid-soluble benzoquinones involved in electron transport and energy production within cellular mitochondria. Coenzyme Q4 increases the fluorescence polarization of perylene incorporated into ubiquinone-depleted bilayer and mitochondrial vesicles prepared from mitochondrial phospholipids. In biochemistry and cell biology research, CoQ4 can be used to study mitochondrial function and the mechanisms of electron transport and redox reactions. Its role in these fundamental processes makes it useful for understanding cellular energy production, aging, and the regulation of oxidative stress. The study of CoQ4 and its interaction with other components of the electron transport chain can provide insights into the design of novel compounds aimed at enhancing mitochondrial efficiency or targeting mitochondrial dysfunctions.