Resonance Raman spectroscopy of chloroperoxidase compound II provides direct evidence for the existence of an iron(IV)-hydroxide.
We report direct evidence for the existence of an iron(IV)-hydroxide. Resonance Raman measurements on chloroperoxidase compound II (CPO-II) reveal an isotope ((18)O and (2)H)-sensitive band at nu(Fe-O) = 565 cm(-1). Preparation of CPO-II in H(2)O using H(2)(18)O(2) results in a red-shift of 22 cm(-1), while preparation of CPO-II in (2)H(2)O using H(2)O(2) results in a red-shift of 13 cm(-1). These values are in good agreement with the isotopic shifts predicted (23 and 12 cm(-1), respectively) for an Fe-OH harmonic oscillator. The measured Fe-O stretching frequency is also in good agreement with the 1.82-A Fe-O bond reported for CPO-II. A Badger's rule analysis of this distance provides an Fe-O stretching frequency of nu(Badger) = 563 cm(-1). We also present X-band electron nuclear double resonance (ENDOR) data for cryoreduced CPO-II. Cryogenic reduction (77 K) of the EPR-silent Fe(IV)OH center in CPO-II results in an EPR-active Fe(III)OH species with a strongly coupled (13.4 MHz) exchangeable proton. Based on comparisons with alkaline myoglobin, we assign this resonance to the hydroxide proton of cryoreduced CPO-II.
Stone
Kari L
KL
Department of Chemistry, Pennsylvania State University, University Park, PA 16802, USA.
Behan
Rachel K
RK
Green
Michael T
MT
D001203:Ascomycota / Q000201:enzymology; D002711:Chloride Peroxidase / Q000737:chemistry*; D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy; D006878:Hydroxides / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D009211:Myoglobin / Q000737:chemistry; D011522:Protons; D013059:Spectrum Analysis, Raman / Q000379:methods*
D006878:Hydroxides; D009211:Myoglobin; D011522:Protons; C031356:hydroxide ion; D007501:Iron; D002711:Chloride Peroxidase