Resonance Raman investigations of chloroperoxidase, horseradish peroxidase, and cytochrome c using Soret band laser excitation

Authors:
  • RRRonald D. Remba
    Ronald D. Remba
  • PCPaul M. Champion
    Paul M. Champion
  • DFDouglas B. Fitchen
    Douglas B. Fitchen
  • RCRobert Chiang
    Robert Chiang
  • LHLowell P. Hager
    Lowell P. Hager
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Abstract
Resonance Raman spectra of the [Caldariomyces fumago] heme protein chloroperoxidase in its native and reduced forms and complexed with various small ions were obtained using later excitation in the Soret region (350-450 nm). Additionally, Raman spectra of horseradish peroxidase, cytochrome P-450cam, and cytochrome c, taken with Soret excitation, are presented and discussed. The data supported previous findings that indicate a strong analogy between the active site environments of chloroperoxidase and cytochrome P-450cam. The Raman spectra of native chloroperoxidase were sensitive to temperature and imply that a high .fwdarw. low spin transition of the heme Fe atom takes place as the temperature is lowered. Unusual peak positions were also found for native and reduced chloroperoxidase and indicated a weakening of porphyrin ring bond strengths due to the presence of a strongly electron-donating axial ligand. Enormous selective enhancements of vibrational modes at 1360 and 674 cm-1 were also observed in some low-spin ferrous forms of the enzyme. These vibrational frequencies were assigned to primary normal modes of expansion of the prophyrin macrocycle upon electronic excitation.

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