Variables in xanthine oxidase-initiated luminol chemiluminescence: implications for chemiluminescence measurements in biological systems.

We tested the effects of generally used chemiluminescence inhibitors on an example of luminol chemiluminescence elicited by xanthine oxidase/hypoxanthine system, and attempted to assess their capabilities in discovering the reaction pathways leading to chemiluminescence. Luminol itself is a xanthine oxidase inhibitor and its concentration affects the reaction mechanism. Maximal chemiluminescence response was observed at luminol concentration inhibiting urate production. Chemiluminescence was totally inhibited by superoxide dismutase, the inhibition by catalase depended on luminol concentration. Ferricytochrome c, a detector of superoxide, either stimulated or inhibited chemiluminescence in a concentration-dependent manner. Chemiluminescence was highly stimulated by peroxidases. A pronounced inhibition of chemiluminescence was caused by chelators; 1 mM desferal and 0.01 mM diethyldithiocarbamate. It is suggested that measurement of luminol chemiluminescence is not a suitable method for discrimination among individual reactive oxygen species and their quantitative determination in biological systems.