STRUCTURAL CHARACTERIZATION OF IRON-BLEOMYCIN BY RESONANCE RAMAN-SPECTROSCOPY

Resonance enhanced modes in the Raman spectra of the ferric, ferrous, and CO-bound ferrous forms of iron bleomycin A(2) (Fe-BLM) have been d etected. Lines in the high-frequency region of the spectrum of the fer ric complex are assigned to the amide I (1608 cm(-1)) and amide II (14 78 cm(-1)) modes of the beta-hydroxyhistidine amide moiety. Two other lines in the spectrum (1388 and 1371 cm(-1)) are assigned to modes of the pyrimidine ring. All of these modes are sensitive to the redox sta te of the iron and the presence of exogenous ligands. The data indicat e that the nitrogen atom of the beta-hydroxyhistidine amide and N1 of the pyrimidine ring are two of the ligands that coordinate iron. The v alence- and ligand-dependent frequency changes of the amide I mode are similar to the valence- and ligand-dependent changes in the yq mode o f iron porphyrins. This suggests the involvement of a delocalized pi-e lectron system in Fe-BLM analogous to that in iron porphyrins. The fir st experimental evidence for hydroxide ligation to iron in Fe(III)-BLM is demonstrated by the presence of an Fe-OH stretching mode at 561 cm (-1). The C-O and the Fe-CO stretching modes of CO-Fe(II)-BLM are loca ted at 1980 and 511 cm(-1), respectively. The frequencies of these mod es, which are typical of those for iron porphyrin and heme protein CO complexes, indicate that the electronic properties of CO-Fe(II)-BLM ar e similar to those of CO-bound iron porphyrins.