Abstract
We have studied the time course of the absorption of bovine liver catalase after pulse radiolysis with oxygen saturation in the presence and absence of superoxide dismutase. In the absence of superoxide dismutase, catalase produced Compound I and another species. The formation of Compound I is due to the reaction of ferric catalase with hydrogen peroxide, which is generated by the disproportionation of the superoxide anion (O-2). The kinetic difference spectrum showed that the other species was neither Compound I nor II. In the presence of superoxide dismutase, the formation of this species was found to be inhibited, whereas that of Compound I was little affected. This suggests that this species is formed by the reaction of ferric catalase with O-2 and is probably the oxy form of this enzyme (Compound III). The rate constant for the reaction of O-2 and ferric catalase increased with a decrease in pH (cf. 4.5 X 10(4) M-1 s-1 at pH 9 and 4.6 X 10(6) M-1 s-1 at pH 5.). The pH dependence of the rate constant can be explained by assuming that HO2 reacts with this enzyme more rapidly than O-2.
Highlights
We have studied the time course of the absorption of horseradish peroxidase [10, 11],and superoxide dismutase bovine liver catalase after pulse radiolysis with oxygen [12,13,14,15]
The formation of Compound Iis due to the reaction of ferric catalase with hydrogen peroxide, which is generated by the disproportionationof the superoxide anion (0;)T.he kinetic difference spectrum showed that the other species wasneither CompoundI nor 11
In the presence of superoxide dismutase,the formationof this species was found to be inhibited, whereas that of CompoundI was littleaffected. This suggests that this species is formed by the reaction of ferric catalase with 0;and is probably the oxy form of this enzyme (Com-We have extended the work by Kono and Fridovich [4], who proposed that the inhibition of catalase by 0; was due to reactions of 0, with ferric catalase and Compound I to yield Compounds I11 and 11, respectively
Summary
We have studied the time course of the absorption of horseradish peroxidase [10, 11],and superoxide dismutase bovine liver catalase after pulse radiolysis with oxygen [12,13,14,15]. In the presence of superoxide dismutase,the formationof this species was found to be inhibited, whereas that of CompoundI was littleaffected This suggests that this species is formed by the reaction of ferric catalase with 0;and is probably the oxy form of this enzyme We have extended the work by Kono and Fridovich [4], who proposed that the inhibition of catalase by 0; was due to reactions of 0, with ferric catalase and Compound I to yield Compounds I11 and 11, respectively. Similar inhibition was observed by Rister and Baehner [5]
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