QUANTITATIVE MODEL OF THE ENHANCEMENT OF PEROXIDASE-INDUCED LUMINOL LUMINESCENCE

Many phenolic compounds are known to enhance the chemiluminescence ass ociated with the horseradish peroxidase-catalyzed oxidation of luminol , but the mechanism of enhancement is still unproved. Using stopped-fl ow spectrophotometry, we have found that a series of luminescence enha ncers react rapidly with the peroxidase reactive intermediates (compou nd I and compound II) supporting the hypothesis that the enhancement i s due to the acceleration of the enzyme turnover. In addition, pulse r adiolysis experiments have shown that the enhancers' phenoxyl radicals oxidize luminol, consistent with a redox mediator role for the enhanc ers. The latter reaction was found to be reversible, showing that enha ncers of low reduction potential, which are efficient in accelerating the enzyme turnover, are also scavengers of luminol radicals and there fore luminescence quenchers. Using these data, a simple model is propo sed which correctly predicts that the efficiency of a phenolic compoun d as luminescence enhancer depends on the reduction potential of the r espective phenoxyl radical according to a bell-shaped function with a maximum at similar to 0.8 V.