AbstractThe key role of coenzyme Q (ubiquinone or Q) is in mitochondrial and prokaryotic energetics. Less well investigated is the basis for its presence in eukaryotic membrane locations other than mitochondria and in plasma where both antioxidant and potentially more targeted roles are indicated. Included in the latter is that of a lipid‐soluble electron transfer intermediate that serves as the transmembrane component of plasma membrane and Golgi apparatus electron transport, which regulates cytosolic NAD+/NADH ratios and is involved in vectorial membrane displacements and in the regulation of cell growth. Important protective effects on circulating lipoproteins and in the prevention of coronary artery disease ensue not only from the antioxidant role of CoQ10 but also from its ability to directly block protein oxidation and superoxide generation of the TM‐9 family of membrane proteins known as age‐related NADH oxidase or arNOX (ENOX3) and their shed forms that appear after age 30 and some of which associate specifically with low‐density lipoprotein particles to catalyze protein oxidation and crosslinking.