Kinetic studies of iron deposition in horse spleen ferritin using H2O2 and O2 as oxidants.
The reaction of horse spleen ferritin (HoSF) with Fe2+ at pH 6.5 and 7.5 using O2, H2O2 and 1:1 a mixture of both showed that the iron deposition reaction using H2O2 is approximately 20- to 50-fold faster than the reaction with O2 alone. When H2O2 was added during the iron deposition reaction initiated with O2 as oxidant, Fe2+ was preferentially oxidized by H2O2, consistent with the above kinetic measurements. Both the O2 and H2O2 reactions were well defined from 15 to 40 degrees C from which activation parameters were determined. The iron deposition reaction was also studied using O2 as oxidant in the presence and absence of catalase using both stopped-flow and pumped-flow measurements. The presence of catalase decreased the rate of iron deposition by approximately 1.5-fold, and gave slightly smaller absorbance changes than in its absence. From the rate constants for the O2 (0.044 s(-1)) and H2O2 (0.67 s(-1)) iron-deposition reactions at pH 7.5, simulations of steady-state H2O2 concentrations were computed to be 0.45 microM. This low value and reported Fe2+/O2 values of 2.0-2.5 are consistent with H2O2 rapidly reacting by an alternate but unidentified pathway involving a system component such as the protein shell or the mineral core as previously postulated [Biochemistry 22 (1983) 876; Biochemistry 40 (2001) 10832].
Lowery
Thomas J
TJ
Department of Chemistry and Biochemistry, Brigham Young University, C100 BNSN, Provo, UT 84602, USA.
Bunker
Jared
J
Zhang
Bo
B
Costen
Robert
R
Watt
Gerald D
GD
D000818:Animals; D001052:Apoferritins / Q000378:metabolism; D002374:Catalase / Q000494:pharmacology; D005293:Ferritins / Q000378:metabolism*; D006736:Horses; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D016877:Oxidants / Q000494:pharmacology*; D010100:Oxygen / Q000378:metabolism*; D013154:Spleen / Q000378:metabolism*
D016877:Oxidants; D005293:Ferritins; D001052:Apoferritins; D006861:Hydrogen Peroxide; D007501:Iron; D002374:Catalase; D010100:Oxygen