Coenzyme Q10 assay arNOX is a coenzyme Q10-inhibited, aging-related external NADH oxidase (ECTO-NOX) protein of the cell surface that is also present in sera and saliva. It is capable of superoxide generation measured as superoxide dismutase-inhibited reduction of ferricytochrome c (Oxidaised cytochrome C). arNOX activity of saliva of older individuals is inhibited by coenzyme Q10. The activity first appears after age 30 to a near maximum at about age 55.