Abstract
The electron paramagnetic resonance spectra of chloroperoxidase Compound I and native enzyme are compared. Upon the formation of Compound I, the g = 2.62, 2.26, and 1.82 signals associated with native enzyme disappear and are replaced by two new EPR signals, a sharp signal at g = 2.008 and a broad signal at g = 1.73. The g = 2.008 signal accounts for only 2% of the theoretical spins while the broad signal at g = 1.73 accounts for 60 to 70% of the theoretical spins in Compound I. The g = 1.73 broad signal is reminiscent of the broad EPR signal associated with horseradish peroxidase Compound I. however, the chloroperoxidase Compound I signal has a significantly different g value. The results suggest that the g = 1.73 signal represents a porphyrin pi cation radical which has a stronger coupling to the heme ferryl iron than is the case with horseradish peroxidase Compound I.
Highlights
Compound I and native enzyme are comthe formationof CompoundI, theg = 2.62, signals associated with native enzyme tinely determined from the absorbance a t 399 nm using a molar absorption coeficient of 8.5 X lo4 M” cm”
A very broad EPR signal centered at g = 1.73 and about, 1600 G. wide has been found to be associated with the formation and decay of contained trace quantities of tightly bound Mn2’
It has been shown by a combination of visible, Mossbauer, EPR, andENDOR spectroscopy that horseradish peroxidase Compound I stores its total of two oxidation equivalents by 1) oxidizing the heme iron from the ferric state to a low spin ferryl species and 2) by removing an electron from one of the porphyrin n orbitals [18, 19]
Summary
Compound I signal has a significantly differengt value. The resuIts suggest that the g = 1.73 signal represents a porphyrin T cation radical which has a stronger coupling to theheme ferry ironthan is the case with ion, 13- [14].In order to increase stability, all peroxide solutions were dissolved in triple distilled water and stored in nalgene flasks. In addition to halogenating activity, chloroperoxidase possesses classical peroxidase [1,2,3,4,5,6]. Of EDTA to carefully dried samples of copper chloride. The freeze-quench standards hadan average packing factor of 0.6 spins/spectra in comparison to 1 spin/speetra for conventionally frozen copper EDTA EPR samples. Chloroperoxidase shares common standard freeze-quench samples into EPR tubeswere no greater than features with the P450cytochromes [7, 11]. Chloroperoxidase forms the classical peroxidase intermediates, Compounds I and I1 [5]. These compounds represent enzyme intermediate states which are two
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
