Stimulation by nitroxides of catalase-like activity of hemeproteins. Kinetics and mechanism

Murali C. Krishna*, Amram Samuni, Junsei Taira, Sara Goldstein, James B. Mitchell, Angelo Russo

*Corresponding author for this work

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Abstract

The ability of stable nitroxide radicals to detoxify hypervalent heme proteins such as ferrylmyoglobin (MbFe(IV)) produced in the reaction of metmyoglobin (MbFe(III)) and H2O2 was evaluated by monitoring O2 evolution, H2O2 depletion, and redox changes of the heme prosthetic group. The rate of H2O2 depletion and O2 evolution catalyzed by MbFe(III) was enhanced by stable nitroxides such as 4-OH-2,2,6,6-tetramethyl-piperidinoxyl (TPL) in a catalytic fashion. The reduction of MbFe(IV) to MbFe(III) was the rate-limiting step. Excess TPL over MbFe(III) enhanced catalase-like activity more than 4-fold. During dismutation of H2O2, [TPL] and [MbFe(IV)] remained constant. NADH caused: (a) inhibition of H2O2 decay; (b) progressive reduction of TPL to its respective hydroxylamine TPL-H; and (c) arrest/inhibition of oxygen evolution or elicit consumption of O2. Following depletion of NADH the evolution of O2 resumed, and the initial concentration of TPL was restored. Kinetic analysis showed that two distinct forms of MbFe(IV) might be involved in the process. In summary, by shuttling between two oxidation states, namely nitroxide and oxoammonium cation, stable nitroxides enhance the catalase mimic activity of MbFe(III), thus facilitating H2O2 dismutation accompanied by O2 evolution and providing protection against hypervalent heme proteins.

Original languageEnglish
Pages (from-to)26018-26025
Number of pages8
JournalJournal of Biological Chemistry
Volume271
Issue number42
DOIs
StatePublished - 1996

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