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Kinetic studies on the oxidation of nitrite by horseradish peroxidase and lactoperoxidase

100%
Gębicka L.
Acta Biochimica Polonica
|
1999
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vol. 46
|
issue 4
919-927
EN
The reaction of nitrite (NO-_2) with horseradish peroxidase and lactoperoxidase was studied. Sequential mixing sopped-flow measeruments gave the following values for the rate constants of the reaction of nitrite with compounds II (oxoferryl heme intermediates) of horseradish peroxidase and lactoperoxidase at pH 7.0, 13.3 ± 0.07 mol^{-1}dm^3s^{-1} and 3.5 ± 0.05 · 10^4mol^{-1}dm^3s^{-1}, respectively. Nitrite, at neutral pH, influenced measurements of activity of lactoperoxidase with typical substrates like 2,2'-azino-bis[ethyl-benzothiazoline-(6)-sulphonic acid] (ABTS), guaiacol or thiocyanate (SCN-). The rate of ABTS and guaiacol oxidation increased linearly with nitrite concentration up to 2.5-5 mmol dm^{-3}. On the other hand, two-electron SCN- oxidation was inhibited in the presence od nitrite. Thus, nitrite competed with the investigated substrates of lactoperoxidase. The intermediate, most probably nitrogen dioxide (*NO_2), reacted more rapidly with ABTS or guaiacol than did lactoperoxidase compound II. It did not, however, effectively oxidize SCN- to OSCN-. NO-_2 did not influence the activity measurements of horseradish peroxidase by ABTS or guaiacol method.
2
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Does the peroxidase-like activity of sodium dodecyl sulphate-modified cytochrome c increase after peroxynitrite or radiation treatment?.

63%
Gębicka L., Didik J.
|
2005
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vol. 52
|
issue 2
551-555
EN
The peroxidase-like activity of cytochrome c is considerably increased by unfolding of the protein. The enhancement of the activity is due to the higher reaction rate of unfolded cytochrome c with hydrogen peroxide, which is the rate-determining step in the peroxidase cycle of cytochrome c (Gębicka, L., 2001, Res Chem Intermed 27, 717-23). In this study we checked whether combined action of two unfolding factors, SDS and peroxynitrite or radiation (hydroxyl radicals), increases the peroxidase-like activity of cytochrome c more than any single treatment alone. Peroxynitrite reacts with SDS-modified cytochrome c in the same way as with native cytochrome c, via intermediate radical products, •OH/•NO2, arising from peroxynitrite homolysis. We found that SDS-modified cytochrome c is much more sensitive to oxidative damage than the native protein. Partial unfolding of cytochrome c by SDS causes the peroxide substrate to have a better access to the heme center. On the other hand, the amino acids located in the vicinity of the active site and/or heme group become accessible for oxidizing radicals. The overall effect observed is that the peroxidase-like activity of SDS-modified cytochrome c decreases with an increase of the concentration of the oxidizing species (peroxynitrite or radiolytically generated hydroxyl radicals). The damage of SDS-modified cytochrome c caused by irradiation is much more significant than that observed after peroxynitrite treatment.
3
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Mechanism of peroxynitrite interaction with cytochrome c.

63%
Gębicka L., Didik J.
|
2003
|
vol. 50
|
issue 3
815-823
EN
Kinetics of the reaction of peroxynitrite with ferric cytochrome c in the absence and presence of bicarbonate was studied. It was found that the heme iron in ferric cytochrome c does not react directly with peroxynitrite. The rates of the absorbance changes in the Soret region of cytochrome c spectrum caused by peroxynitrite or peroxynitrite/bicarbonate were the same as the rate of spontaneous isomerization of peroxynitrite or as the rate of the reaction of peroxynitrite with bicarbonate, respectively. This means that intermediate products of peroxynitrite decomposition, ·OH/·NO2 or, in the presence of bicarbonate, CO3-·/·NO2, are the species responsible for the absorbance changes in the Soret band of cytochrome c. Modifications of the heme center of cytochrome c by radiolytically produced radicals, ·OH, ·NO2 or CO3-·, were also studied. The absorbance changes in the Soret band caused by radiolytically produced ·OH or CO3-· were much more significant that those observed after peroxynitrite treatment, compared under similar concentrations of radicals. ·NO2 produced radiolytically did not interact with the heme center of cytochrome c. Cytochrome c exhibited an increased peroxidase-like activity after reaction with peroxynitrite as well as with radiolytically produced ·OH, ·NO2 or CO3-· radicals. This means that modification of protein structure: oxidation of amino acids and/or tyrosine nitration, facilitates reaction of H2O2 with the heme iron of cytochrome c, followed by reaction with the second substrate.
4
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Scavenging of oxygen radicals by heme peroxidases

32%
Gębicka L., Gębicki J. L.
Acta Biochimica Polonica
|
1996
|
vol. 43
|
issue 4
673-678
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