Abstract
Renewed interest in the metabolism of O2 radicals and H2O2 stems from awareness of their roles, for example, in BPD, WBC function, and certain hemolytic anemias. Two means for disposal of H2O2 are: (a) catalase and (b) the glucose-6-phosphate dehydrogenase (G6PD), NADPH, glutathione reductase/peroxidase pathway. As reflected in the present study by initial rates in the spectrophotometric assay of Aebi, purified catalase from human red cells and bovine liver underwent partial inactivation when diluted to nanomolar concentrations at pH 7. Inactivation occurred despite the presence of bovine albumin and the use of plastic containers. The inactivation was prevented, but not promptly reversed, by the addition of NADPH. This effect seems to be a second type of protection of catalase by NADPH. Kirkman & Gaetani recently found that catalase contains tightly bound NADPH, which is slowly oxidized in the process of preventing and reversing the inactivation (formation of compound II) of catalase by its own substrate, H2O2 (J. Biol. Chem. 262, in press, 1987). Human catalase came to be regarded as a “fossil enzyme” as a result of the relatively benign nature of acatalasemia and the known sensitivity to drug- induced peroxidative stress of G6PD-deficient red cells, a deficiency affecting over 100 million people. Knowledge of catalase-NADPH interaction, however, allows re-interpretation of earlier studies and leads to the conclusion that human catalase and pathway (b) are both responsible for H2O2 removal. Both are dependent on NADPH, which explains the particular susceptibility of G6PD-deficient red cells to peroxidative stress.
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Kirkman, H. METABOLIC IMPLICATIONS OF CATALASE–BOND NADPH. Pediatr Res 21 (Suppl 4), 300 (1987). https://doi.org/10.1203/00006450-198704010-00797
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DOI: https://doi.org/10.1203/00006450-198704010-00797