Resonance Raman spectra of Pseudomonas cytochrome c peroxidase

Abstract

Resonance Raman spectra of ferric, ferrous and ferrous-carbonyl forms of Pseudomonas cytochrome c peroxidase are presented. The porphyrin ring vibration frequencies are compared with those of other heme proteins which are in well defined spin and oxidation states. Both the native oxidized and the reduced forms of the enzyme show two sets of Raman lines, one having a low-spin and the other a high-spin character. Resolved bands can be assigned to heme c and heme c', the low-spin and the high-spin moiety of the enzyme, respectively. The low-spin heme moiety of the ferric enzyme is concluded to have an imidazole-nitrogen : heme-iron : methionine-sulphur hemochrome structure, whereas in the ferrous enzyme the methionine-sulphur ligation is exchanged with the nitrogen of histidine or lysine (N epsilon). The Raman spectra indicate that the high-spin ferric heme consists of a mixture of a five-coordinated form and a six-coordinated form with a carboxylate group as a ligand. In the reduced enzyme the high-spin heme is five-coordinated. The Raman spectrum of the carbonyl derivative of Pseudomonas cytochrome c peroxidase indicates that the compound has an electron structure similar to that of carboxyhemoglobin and carboxymyoglobin. The data confirm earlier results that the two heme moieties of the enzyme are bound to the apoprotein by covalent thioether bonds as in c-type cytochromes.