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.

scholarly journals Electron-paramagnetic-resonance studies on a photochemically produced species of horseradish peroxidase compound I

1977 ◽  
Vol 167 (1) ◽  
pp. 31-37 ◽  
Author(s):  
A R McIntosh ◽  
M J Stillman
Keyword(s):  
Electron Paramagnetic Resonance ◽  
New Species ◽  
Horseradish Peroxidase ◽  
Room Temperature ◽  
Resonance Signal ◽  
Compound I ◽  
Radical Species ◽  
Strong Electron ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic

Strong electron-paramagnetic-resonance signals in the g = 2.00 region were detected after irradiation of horseradish peroxidase Compound I at temperatures of 10 and 100 K. These signals establish the presence of new free-radical species in the peroxidase system. The new species are interpreted in terms of a haem-photosensitized oxidation of the protein's peptide groups close to the Compound I radical site. On warming to room temperature, the radicals decayed irreversibly to a species having a weak asymmetric electron-paramagnetic-resonance signal at 100 K, which could still be observed after incubation at room temperature for more than 1 h.

Titration Study of Guaiarcol Oxidation by Horseradish Peroxidase

1975 ◽  
Vol 53 (6) ◽  
pp. 649-657 ◽  
Author(s):  
Marius Santimone
Keyword(s):  
Hydrogen Peroxide ◽  
Electron Transfer ◽  
Low Temperature ◽  
Horseradish Peroxidase ◽  
Catalytic Amount ◽  
Reaction Scheme ◽  
General Mechanism ◽  
Compound I ◽  
Compound Ii ◽  
Titration Study

Titration of guaiacol by hydrogen peroxide in the presence of a catalytic amount of horseradish peroxidase shows that the reduction of hydrogen peroxide proceeds by the abstraction of two electrons from a guaiacol molecule. In the same way, it can be demonstrated that 0.5 mol of guaiacol can reduce, at low temperature, 1 mol of peroxidase compound I to compound II. Moreover, the reaction between equal amounts of compound I and guaiacol at low temperature produces the native enzyme. A reaction scheme is proposed which postulates that two electrons are transferred from guaiacol to compound I giving ferriperoxidase and oxidized guaiacol with the intermediary formation of compound II. The direct two-electron transfer from guaiacol to compound I without a dismutation of product free radicals must be considered as an exception to the general mechanism involving a single-electron transfer.

Low temperature MCD study of the species formed by photolysis of horseradish peroxidase compound I

1983 ◽  
Vol 79 ◽  
pp. 115-116 ◽  
Author(s):  
William R. Browett ◽  
Zbigniew Gasyna ◽  
Martin J. Stillman
Keyword(s):  
Low Temperature ◽  
Horseradish Peroxidase ◽  
Compound I
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