METALLOBLEOMYCINS - ELECTRON-SPIN RESONANCE STUDY ON NITROSYL COMPLEX OF IRON(II)-BLEOMYCIN

The ESR spectrum of the bleomycin-Fe(II)NO complex shows rhombic symmetry with a triplet hyperfine interaction in the gz signal, and its ESR parameters have been compared with those of the ferrous-NO complexes of hemoproteins. The substitution of 14NO by 15NO gives the transition from a triplet to a doublet in the gz absorption with a concomitant change in the nitrogen hyperfine constant. The addition of DNA to the ferrous-NO complex of bleomycin induces the greater separation of the gx and gy absorptions in comparison with the original ESR spectrum. The present three-line gz signal for the bleomycin-Fe(II)-NO complex is indicative of weakened fifth axial nitrogen ligand-to-iron bonding with concomitantly stronger NO-to-iron bonding. On the other hand, the ESR feature of the bleomycin-Fe(III) complex is typical of the rhombic low-spin type, and no stable ferric-NO complex of bleomycin is formed. © 1979.