ECTO-NOX (because of their cell surface location) proteins comprise a family of NAD(P)H oxidases of plants and animals that exhibit both oxidative and protein disulfide isomerase-like activities. The two biochemical activities, hydroquinone [NAD(P)H] oxidation and protein disulfide--thiol interchange alternate, a property unprecedented in the biochemical literature. A tumor-associated ECTO-NOX (tNOX) is cancer-specific and drug-responsive. The constitutive ECTO-NOX (CNOX) is ubiquitous and refractory to drugs. The physiological substrate for the oxidative activity appears to be hydroquinones of the plasma membrane such as reduced coenzyme Q10. ECTO-NOX proteins are growth-related and drive cell enlargement. Also indicated are roles in aging and in neurodegenerative diseases. The regular pattern of oscillations appears to be related to alpha-helix-beta-structure transitions and serves biochemical core oscillator of the cellular biological clock. Period length is independent of temperature (temperature compensated) and synchrony is achieved through entrainment.