PROTOPORPHYRIN-IX POTENTIATES HORSERADISH PEROXIDASE-CATALYZED OXIDATION OF NADH - INVOLVEMENT OF ENZYME-PORPHYRIN INTERACTION

Protoporphyrin IX potentiates horseradish peroxidase-catalyzed hydroge n peroxide-mediated NADH oxidation, but the porphyrin cannot change th e enzyme-catalyzed o-dianisidine oxidation. Spectrofluorimetric studie s reveal that an interaction occurs between horseradish peroxidase and protoporphyrin IX. The interaction is predominantly hydrophobic and e ntropy-driven endothermic process. This interaction may influence the potentiation effect of the protoporphyrin IX on horseradish peroxidase -catalyzed NADH oxidation because the latter has a positive correlatio n with the extent of binding of the protein with the porphyrin.