Lignin peroxidase: resonance Raman spectral evidence for compound II and for a temperature-dependent coordination-state equilibrium in the ferric enzyme

Publisher Website
Google Scholar
Abstract
Resonance Raman (RR) spectroscopy of lignin peroxidase (ligninase, diarylpropane oxygenase) from the basidiomycete Phanerochaete chrysosporium suggests two different coordination states for the native ferric enzyme. Evidence for a high-spin, hexacoordinate ferric protoporphyrin IX was presented by Andersson et al. [Andersson, L. A., Renganathan, V., Chiu, A. A., Loehr, T. M., and Gold, M. H. (1985) J. Biol. Chem. 260, 6080-6087], whereas Kuila et al. [Kuila, D., Tien, M., Fee, J. A., and Ondrias, M. R. (1985) Biochemistry 24, 3394-3397] proposed a high-spin, pentacoordinate ferric system. Because the two RR spectral studies were perfomed at different temperatures, we explored the possibility that lignin peroxidase might exhibit temperature-dependent coordination-state equilibria. Resonance Raman results presented herein indicate that this hypothesis is indeed correct. At or near 25.degree. C, the ferric iron of lignin peroxidase is predominantly high spin, pentacoordinate; however, at .ltoreq. 2.degree. C, the high-spin, hexacoordinate state dominates, as indicated by the frequencies of well-documented spin- and coordination-state marker bands for iron protoporphyrin IX. The temperature-dependent behavior of lignin peroxidase is thus similar to that of cytochrome c peroxidase (CCP). Furthermore, lignin peroxidase, like horseradish peroxidase (HRP) and CCP, clearly has a vacant coordination site trans to the native fifth ligand at ambient temperature. High-frequency RR spectra of compound II of lignin peroxidase are also presented. The observed shifts to higher frequency for both the oxidation-state marker band .nu.4 and the spin- and coordination-state marker band .nu.10 are similar to those reported for the compound II forms of HRP and lactoperoxidase and for ferryl myoglobin. These observations are consistent with a low-spin, hexacoordinate Fe(IV).dbd.O structure for lignin peroxidase compound II.