The non-photosensitized potentiation by the photosensitizer hematoporphyrin of the horseradish peroxidase-catalyzed H2O2-mediated oxidation of NADPH to NADP+.

Horseradish peroxidase is known to oxidize NADPH in a reaction initiated by hydrogen peroxide. The present study demonstrates that the photosensitizer hematoporphyrin acting in a non-photodynamic manner, has a marked potentiating effect on the nucleotide oxidation rate. Over 90 percent of the NADPH oxidation product is enzymatically active NADP+. The ratio of NADPH oxidized to NADPH added indicates the existence of a chain reaction. It is suggested that the enzymatic generation of hematoporphyrin transients which are usually generated photodynamically, may be responsible for the acceleration in rate of reduced nucleotide oxidation.