| Abstract
| - The ferritins are a class of iron storage and detoxification proteins that play a central role inthe biological management of iron. These proteins have a catalytic site, “the ferroxidase site”, located onthe H-type subunit that facilitates the oxidation of Fe(II) to Fe(III) by O2. Measurements during the past10 years on a number of vertebrate ferritins have provided evidence that H2O2 is produced at this diironferroxidase site. Recently reported experiments using three different analytical methods with horse spleenferritin (HoSF) have failed to detect H2O2 production in this protein [Lindsay, S., Brosnahan, D., andWatt, G. D. (2001) Biochemistry40, 3340−3347]. These findings contrast with earlier results reportingH2O2 production in HoSF [Xu, B., and Chasteen, N. D. (1991) J. Biol. Chem. 266, 19965−19970]. Herea sensitive fluorescence assay and an assay based on O2 evolution in the presence of catalase were usedto demonstrate that H2O2 is produced in HoSF as previously reported. However, because of the relativelyfew H-chain ferroxidase sites in HoSF and the reaction of H2O2 with the protein, H2O2 is more difficultto detect in this ferritin than in recombinant human H-chain ferritin (HuHF). The proper sequence ofaddition of reagents is important for measurement of the total amount of H2O2 produced during theferroxidation reaction.
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