RESONANCE RAMAN INVESTIGATION OF CYANIDE LIGATED BEEF-LIVER AND ASPERGILLUS-NIGER CATALASES

Resonance Raman spectroscopy has been used to investigate the properties of cyanide-bound beef liver catalase (BLC) and Aspergillus niger catalase (ANC) in the pH range 4.9-11.5. Evidence has been obtained for the binding of cyanide to both BLC and ANC in two binding geometries. The first conformer, exhibiting the nu[Fe-CN] stretching mode at a higher frequency than the delta[Fe-C-N] bending mode, exists as an essentially linear Fe-C-N linkage. For both BLC-CN and ANC-CN, the nu[Fe-CN] and delta[Fe-C-N] frequencies of this conformer were practically identical and observed at similar to 434 and similar to 413 cm(-1), respectively. The second conformer exhibits a nu[Fe-CN] mode at lower frequency than the delta[Fe-C-N] mode, and is thus characteristic of a bent Fe-C-N linkage. The nu[Fe-CN] and delta[Fe-C-N] modes were identified at 349 and 445 cm(-1), respectively, for BLC-CN, and at 350 and 456 cm(-1), respectively, for ANC-CN. The two conformers persist in the pH range 4.9-11.5. Furthermore, upon raising the pH to 11.5, the nu[Fe-CN] mode of the linear conformer of BLC-CN downshifts to 429 cm(-1) while that of the bent conformer remains unchanged. The observed pH-dependent shift is attributed to the deprotonation of a distal-side amino acid residue, probably a distal histidine, The Fe-C-N axial vibrations of the two conformers identified for ANC-CN did not show any significant pH-dependent shifts, indicating a more stable hydrogen bonding interaction relative to BLC-CN.