title: Resonance Raman investigation of cyanide ligated beef liver and Aspergillus niger catalases.
abstract: 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 approximately 434 and approximately 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.
authors.affiliation: Chemistry Department, Marquette University, Milwaukee, Wisconsin 53233, USA.
authors.forename: J
authors.initials: J
authors.lastname: al-Mustafa
authors.forename: M
authors.initials: M
authors.lastname: Sykora
authors.forename: J R
authors.initials: JR
authors.lastname: Kincaid
mesh_terms: D000818:Animals; D001234:Aspergillus niger / Q000201:enzymology; D002374:Catalase / Q000737:chemistry*; D002417:Cattle; D003486:Cyanides / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman
chemical_list: D003486:Cyanides; D002374:Catalase