Dept. of Biochemistry
Oregon Graduate Center
Amicyanin is a blue copper protein which functions as a redox mediator in Paracoccus denitrificans. Its resonance Raman (RR) spectrum exhibits intense peaks in the 300-500 cm [superscript -1] region, suggesting that the copper is ligated to a cysteine thiolate. Most of the RR peaks shift 0.5-1.5 cm[superscript -1] to lower energy upon equilibration with D2O, indicating that the cysteine sulfur is hydrogen-bonded to the polypeptide backbone. The high energy of the fundamental RR bands suggests a short Cu-S (Cys) bond distance and their multiplicity implies coupling of Cu-S stretch with internal ligand vibrational modes. These characteristics suggest a distorted trigonal copper site similar to that of azurin and plastocyanin. Hemcyanin, a binuclear copper protein, exhibits RR peaks at 747 cm[superscript -1] and 550 cm[superscript -1] which have been assigned to Î½(0-0) and Î½(Cu-O2), respectively, of a coordinated peroxide. Neither peak show any frequency shift when the protein is equilibrated in D2O. This implies the absence of hydrogen bond between the peroxide oxygens and the protein. In addition, neither the peroxide-related vibrations at 747 and 550 cm[superscript -1] nor the copper-imidazole vibrations at 230, 269, and 313 cm[superscript -1] show any sensitivity to solvent [superscript 18]O-substitution. This suggest that each of these is a relatively pure vibrational mode and that if a hydroxide bridging ligand is present, its vibrations are not enhanced by excitation within the 345 or 565 nm absorption bands. Catalase is a heme enzyme responsible for the disproportionation of hydrogen peroxide. The crystal structures of homologous enzymes from bovine liver and Penicillium vitale show tyrosine as an axial ligand to the iron. Resonance Raman spectra of catalase from mammalian, fungal, and bacterial sources were found to be characteristic of a high spin pentacoordinate Fe (III) heme. In addition, new peaks at ~1610 and 1245 cm[superscript -1] were observed which are characteristic of tyrosinate ligation. Thus, the tyrosine ligand in mammalian and fungal catalases can be detected by RR spectroscopy and a similar structure is likely for bacterial catalase, as well.
Sharma, Kamala Devi, "Identification of metal ligands in amicyanin, hemocyanin, and catalase by resonance raman spectroscopy" (1988). Scholar Archive. 272.