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|Title:||The Free Radical Nature of Compound I From Horseradish Peroxidase and Chloroperoxidase|
|Author(s):||Rutter, Rick J.|
|Department / Program:||Biochemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Compound Is were prepared from Horseradish Peroxidase (HRP), Chloroperoxidase (CPO), mesohemin substituted Horseradish Peroxidase (M-HRP) and deuterohemin substituted Horseradish Peroxidase. The Compound Is were analyzed by visible absorption, electron paramagnetic resonance (EPR), Mossbauer and electron nuclear double resonance (ENDOR) spectra. These spectral techniques were used to prove that one of the two oxidation equivalents associated with Compound I consists of a porphyrin centered pi-cation radical.
Titration of the EPR and visible absorption spectra associated with Compound I formation and ENDOR spectra of deuterium substituted hemin demonstrated unequivocally that HRP Compound I has a pi-cation porphyrin centered radical associated with it.
A g = 1.73 EPR signal was found to be associated with CPO Compound I. This EPR signal accounted for the theoretical spins which should be associated with Compound I assuming one unpaired spin per heme group. CPO Compound I Mossbauer spectra showed a strong magnetic broadening which could be accounted for by a strong interaction of a radical with the proven low spin ferryl iron center.
EPR and Mossbauer spectra of M-HRP Compound I showed that it is very similar to HRP Compound I in conflict with the predictions of others. The EPR spectrum of D-HRP Compound I did not detect a major radical signal.
It was proven that HRP, CPO and M-HRP Compound Is utilize a free radical, which is porphyrin centered, to store one of the two oxidation equivalents associated with Compound I formation.
Oxygen 17 ENDOR spectroscopy was utilized to show that one of the oxygens from the peroxide used to form HRP and CPO Compound Is remains covalently attached to the intermediate. This peroxide derived oxygen associated with Compound I was shown to be non-exchangeable with the solvent water.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.
|Date Available in IDEALS:||2014-12-15|