A comparison by magnetic circular dichroism of compound X and compound II of horseradish peroxidase

Abstract

The chlorite product of horseradish peroxidase, compound X, is shown by magnetic circular dichroism (MCD) spectroscopy in the temperature range 1.6–50 K to have a very similar haem structure to compound II under the same conditions (pH 10.7). Both are concluded to contain the Fe(IV)=0 group. The MCD spectrum also detects an unusual species, absorbing at wavelengths between 600 and 750 nm, that has magnetic properties different from those of the ferryl haem group. It is suggested that this is a species at the same oxidation level as ferryl haem but with the porphyrin ring having suffered a one‐electron oxidation, i.e. [Fe(III) P.+].

Analysis of the optical absorption and magnetic-circular-dichroism spectra of peanut peroxidase: electronic structure of a peroxidase with biochemical properties similar to those of horseradish peroxidase

“…The spectral properties of these species have been studied extensively in order to interpret the role of the electronic structure of the iron and the porphyrin ring in the observed enzymatic chemistry (Strickland et al, 1968;Fajer et al, 1973;Stillman et al, 1975Dunford and Stillman, 1976;Morishima and Ogawa, 1978;Browett and Stillman, 1979, 1981aDolphin, 1981;Hanson et al, 1981;Teraoka et al, 1982;Browett et al, 1983a,b;Sievers et al, 1983;Fujita et al, 1983;Ohlsson et al, 1984;Oertling and Babcock, 1985;van Wart and Zimmer, 1985;Penner-Hahn et al, 1986;Foote et al, 1987;Oertling et al, 1987;Ogura and Kitagawa, 1987;Browett et al, 1988;Gasyna et al, 1988a;Dawson et al, 1991;Loew et al, 1991;Du et al, 1991;Du and Loew, 1992). The absorption spectra of HRP I and catalase I have long puzzled spectroscopists, as these spectra are quite unique.…”