title: Resonance Raman investigation of ferric iron in horseradish peroxidase and its aromatic donor complexes at room and low temperatures.
abstract: Resonance Raman (RR) spectra of the acidic form of FeIII horseradish peroxidase (HRP) were obtained at room and low temperatures using B- and Q-band excitation. At 296 K, HRP exhibits two sets of porphyrin skeletal stretching frequencies which are attributed to a thermal mixture of 5- and 6-coordinate high-spin FeIII states. When the temperature is lowered, the observed bands shift to higher frequencies, and these are assigned to intermediate- and low-spin states. Addition of 40% glycerol has no effect on the spectra at 296 K, but at 20 K, all four frequency sets are observed corresponding to the two forms observed at room and low temperature in the absence of glycerol. The 296 K RR spectrum of the HRP-hydroquinone complex is similar to that of free HRP, but conversion to the intermediate- and low-spin states is complete at a higher temperature than in the free enzyme. Addition of benzohydroxamic acid (BHA) to HRP shifts the RR frequencies to those corresponding to a 6-coordinate high-spin species at both room and low temperature. Two upsilon (C = C) stretching modes are observed for HRP and its donor complexes, indicating that the vinyl groups are inequivalent. On BHA binding, one of the vinyl modes and upsilon 37 (Eu) are enhanced, suggesting symmetry lowering of the heme site.
authors.affiliation: Dipartimento di Chimica, Università di Firenze, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Smulevich
authors.forename: A M
authors.initials: AM
authors.lastname: English
authors.forename: A R
authors.initials: AR
authors.lastname: Mantini
authors.forename: M P
authors.initials: MP
authors.lastname: Marzocchi
mesh_terms: D000818:Animals; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism*; D005990:Glycerol; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006873:Hydroquinones / Q000378:metabolism; D006877:Hydroxamic Acids / Q000378:metabolism; D013059:Spectrum Analysis, Raman; D013696:Temperature; D014753:Vinyl Compounds / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D006873:Hydroquinones; D006877:Hydroxamic Acids; D014753:Vinyl Compounds; D006735:Horseradish Peroxidase; C006696:benzohydroxamic acid; D005990:Glycerol; C031927:hydroquinone