Superoxide generation of phagocytes and nonphagocytic cells

Phagocytes release high amounts of reactive oxygen intermediates upon contact with appropriate stimuli into the environment as an important function in the immune defence against infectious agents. On the other hand nonphagocytic cells release low amounts upon stimulation, which have important functions in the inter- and intracellular signal transduction. Both systems represent a class of isoenzymes making a specific regulation possible. Fibroblasts, hepatocytes, and HeLa cells possess a superoxide system which shows higher activity with NADH than NADPH. The enzyme was purified to homogeneity in an active form, showed a molecular mass of 84 kDa and possessed a flavin and low-potential cytochrome b558.