Absorption and Raman spectroscopy study of cyt c-thiol complexes in acidic solutions

Absorption UV-VIS and pre-resonance Raman spectra of acidic cyt c solutions with a series of thiols added (thiophenol, n-propanethiol, isopropanethiol, L-cysteine, dithiothreitol, 2-mercaptoethanol, N-acetyl-L-cysteine, p-acetamidothiophenol, 2-mercaptoethanamine, thioglycolic acid and mercaptopropionic acid), are presented. Interactions of cyt c molecule with the thiols were studied with the aim to identify binding of the thiols with the cyt c heme as its iron axial ligands. Absorption and Raman spectra showed some correlation between maxima of 700 nm region absorption band (typical for Fe-S axial bond in cyt c heme) and also wave numbers of spin state marker and axial ligand sensitive Raman bands on one, and pKa constant values of appropriate thiols on the other hand. These results imply thiol replacement of Met-80 from axial bond with heme iron and suggest that the force of Fe-L-cysteine axial bond is very close to the native axial bond (Fe-Met) for cyt c in neutral solution.