The function of NADPH bound to Catalase.

NADPH bound to each Catalase subunit was replaced by NADP+ or by the dehydrogenases inhibitor 3-amino-pyridine-adenine dinucleotide phosphate (AADP). The comparison of the three enzyme forms with respect to the capability to dismutate H2O2, or to oxidize ethanol by a peroxidation process using peroxoacetic acid, showed that the enzyme activity is approximately unchanged whatever the nucleotide bound. On the contrary, the dismutation of peroxoacetic acid drops to zero when NADPH is replaced either by the oxidized NADP+ or by the inhibitor AADP. The spectral changes induced by peroxoacetic acid at the heme Soret region indicate that the three enzyme types are quickly oxidized to Compound I [FeV(O)] and successively reduced by two monoelectron intramolecular reactions leading to Compound II [FeIV(OH)] and finally to the resting state (FeIII). Therefore NADPH bound to Catalase is not essential to catalyze peroxidation processes or H2O2 dismutation, but it is essential to prevent the enzyme denaturation and to catalyze dismutation of peroxides other than H2O2.