title: Resonance Raman spectroscopy study of change of iron spin state in horseradish peroxidase C induced by removal of calcium.
abstract: Resonance Raman spectroscopy is used to probe the effect of calcium depletion on the heme group of horseradish peroxidase C at pH 8. Polarized Raman spectra are recorded with an argon ion laser at eight different wavelengths to provide a sound database for a reliable spectral decomposition. Upon calcium depletion, the spectrum is indicative of a predominantly pentacoordinated high spin state of the heme iron coexisting with small fractions of hexacoordinated high and low spin states. The dominant quantum mixed spin state of native ferric horseradish peroxidase, which is characteristic for class III peroxidases, is not detectable in the spectrum of the enzyme with partial distal Ca(2+) depletion. The quenching of the quantum mixed spin state and the predominance of the pentacoordinated high spin state are likely to arise from distortions induced by distal calcium depletion, which translates into a weaker Fe-N(epsilon)(His) bond and a more tilted imidazole. A correlation is proposed between the lower enzyme activity and the elimination of the pentacoordinated quantum mixed state upon Ca(2+) depletion.
authors.affiliation: Department of Chemistry, University of Puerto Rico, Río Piedras Campus, P.O. Box 23346, San Juan, Puerto Rico 00931, USA.
authors.forename: Qing
authors.initials: Q
authors.lastname: Huang
authors.forename: Monique
authors.initials: M
authors.lastname: Laberge
authors.forename: Krisztian
authors.initials: K
authors.lastname: Szigeti
authors.forename: Judit
authors.initials: J
authors.lastname: Fidy
authors.forename: Reinhard
authors.initials: R
authors.lastname: Schweitzer-Stenner
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000302:isolation & purification* / Q000378:metabolism; D006418:Heme / Q000737:chemistry*; D006735:Horseradish Peroxidase / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman / Q000379:methods*; D014466:Ultraviolet Rays
chemical_list: D006418:Heme; D007501:Iron; D006735:Horseradish Peroxidase; D002118:Calcium