Calculated spin densities and quadrupole splitting for model horseradish peroxidase compound I: evidence for iron(IV) porphyrin (S = 1) .pi. cation radical electronic structure

1980 ◽  
Vol 102 (19) ◽  
pp. 6173-6174 ◽  
Author(s):  
Gilda H. Loew ◽  
Zelek S. Herman
Keyword(s):  
Electronic Structure ◽  
Horseradish Peroxidase ◽  
Quadrupole Splitting ◽  
Cation Radical ◽  
Compound I ◽  
Spin Densities

scholarly journals Scavenging of oxygen radicals by heme peroxidases.

1996 ◽  
Vol 43 (4) ◽  
pp. 673-678 ◽  
Author(s):  
L Gebicka ◽  
J L Gebicki
Keyword(s):  
Horseradish Peroxidase ◽  
Hydroxyl Radicals ◽  
Superoxide Radical ◽  
Cation Radical ◽  
Compound I ◽  
Superoxide Radical Anion ◽  
Form Compound ◽  
Activity Loss ◽  
Heme Peroxidases ◽  
Compound Ii

The reactions of two heme peroxidases, horseradish peroxidase and lactoperoxidase and their compounds II (oxoferryl heme intermediates, Fe(IV) = O or ferric protein radical Fe(III)R.) and compounds III (resonance hybrids [Fe(III)-O2-. Fe(II)-O2] with superoxide radical anion generated enzymatically or radiolytically, and with hydroxyl radicals generated radiolytically, were investigated. It is suggested that only the protein radical form of compound II of lactoperoxidase reacts with superoxide, whereas compound II of horseradish peroxidase, which exists only in oxoferryl form, is unreactive towards superoxide. Compound III of the investigated peroxidases does not react with superoxide. The lactoperoxidase activity loss induced by hydroxyl radicals is closely related to the loss of the ability to form compound I (oxoferryl porphyrin pi-cation radical, Fe(IV) = O(Por+.) or oxoferryl protein radical Fe(IV) = O(R.)). On the other hand, the modification of horseradish peroxidase induced by hydroxyl radicals has been reported to cause also restrictions in substrate binding (Gebicka, L. & Gebicki, J.L., 1996, Biochimie 78, 62-65). Nevertheless, it has been found that only a small fraction of hydroxyl radicals generated homogeneously does inactivate the enzymes.

scholarly journals The formation of ferric haem during low-temperature photolysis of horseradish peroxidase Compound I

1987 ◽  
Vol 246 (3) ◽  
pp. 659-668 ◽  
Author(s):  
N Foote ◽  
P M A Gadsby ◽  
M J Berry ◽  
C Greenwood ◽  
A J Thomson
Keyword(s):  
Electronic Structure ◽  
Free Radical ◽  
Low Temperature ◽  
Horseradish Peroxidase ◽  
Spectral Features ◽  
Photolysis Product ◽  
Compound I ◽  
Radical Species ◽  
Step Process ◽  
Peroxide Compound

Illumination at low temperature of the peroxide compound of horseradish peroxidase (HRP-I) causes partial conversion of the haem electronic structure from a ferryl-porphyrin radical species into a low-spin ferric state. Magnetic-c.d. (m.c.d.) and e.p.r. spectral features of the photolysis product are almost identical with those of the alkaline form of ferric HRP, proposed on the basis of its near-i.r. m.c.d. spectrum to be a Fe(III)-OH species. The ferric product of HRP-I photolysis also contains free-radical e.p.r. signals. Conversion of HRP-I into the Fe(III)-OH species, which requires transfer of a proton and two electrons from the protein, is shown to be a two-step process.

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