title: Low-temperature magnetic circular dichroism studies of the photoreaction of horseradish peroxidase compound I.
abstract: Horseradish peroxidase (HRP) compound I is photolabile at all temperatures between room temperature and 4 K. The photoredox reaction has been studied in frozen glassy solutions by using optical absorption and magnetic circular dichroism spectra following photolysis of HRP compound I with visible-wavelength light at 4.2 and 77 K. The photochemical process is characterized as a concerted two-electron transfer reaction which results in the conversion of the Fe(IV) heme pi-cation radical species of HRP compound I into a low-spin Fe(III) heme species. This reaction occurs even when photolysis is carried out at 4.2 K. Spectra recorded between 4.2 and 80 K for the low-spin ferric hydroxide complex of HRP closely resemble the data measured for the photochemical product. The proposed mechanism for the photoreaction is (formula; see text) No evidence is found for the formation of an Fe(II) heme at these temperatures.
authors: Department of Chemistry, University of Western Ontario, London, Canada.
authors: Z
authors: Z
authors: Gasyna
authors: W R
authors: WR
authors: Browett
authors: M J
authors: MJ
authors: Stillman
mesh_terms: D002942:Circular Dichroism; D004579:Electron Transport; D004795:Enzyme Stability; D005615:Freezing; D006735:Horseradish Peroxidase / Q000378:metabolism*; D010544:Peroxidases / Q000378:metabolism*; D010782:Photolysis; D011487:Protein Conformation
chemical_list: D006735:Horseradish Peroxidase; D010544:Peroxidases