Characterization of Acridancarboxylic Acid Derivatives as Chemiluminescent Peroxidase Substrates

A new class of peroxidase substrates has been developed which produces chemiluminescence upon enzymatic oxidation. A wide variety of N-alkylacridancarboxylic acid derivatives including esters, thioesters, and sulfonamides are efficiently oxidized by a peroxidase and a peroxide to enzymatically produce the corresponding chemiluminescent acridinium compound. In conjunction with a peroxidase enhancer, continuous light emission with high light intensities and an extended duration are produced. Alternately, an appropriately designed acridan substrate produces a stable acridinium ester intermediate which can be accumulated and the chemiluminescence elicited as a burst of light by raising the pH. The effects of leaving groups and substitution on the acridan ring on the mechanism of light production are discussed. Peroxidase-catalyzed oxidation in the presence of a peroxide permits the detection of enzyme with subattomolar sensitivity and a broad linear dynamic range.