• Spectroscopy and Spectral Analysis
  • Vol. 42, Issue 3, 821 (2022)

Abstract

The study of electron transfer in life has attracted much attention, and the research on the electron transfer of proteins and enzymes has become a hot spot. However, electron transfer may be an effective way to explain this mechanism. The detailed mechanism of photoinduced heme protein reduction is still unclear. In this paper, UV-visible absorption spectroscopy, steady-state fluorescence spectroscopy and circular dichroism spectroscopy were used to study the effects of different UV wavelengths systematically, pH, amino acids,Glutathione and Imidazoleon the photoreduction of Cyt b5 in vitro near-physiological environment to clarify the photoreduction mechanisms of Cyt b5 which wasn’t proposed by the traditional methods. The results show that ferric cytochrome b5 can be photoreduced to the ferrous state by direct photoexcitation in the near-ultraviolet region. In this study, we studied the mechanism and facilitating conditions for photoreduction. Based on the sort band blue-shifted of 412 nm and absorbance intensity increase of Q band 556 nm, Cyt b5-Fe in phosphate-buffered was photoreduced to Cyb5-Fe similar to the action of a chemical reducing agent occurs. Considering that the fixed wavelength, pH values, amino acids and ligands of photoreduction were irradiated by 280 nm light, Cyt b5 had the strongest reduction degree. Under 280 nm alkaline conditions, Cyt b5 had the strongest reduction degree; glutathione and imidazole promoted the photoreduction reaction by providing electron and hydrogen donors; free Met in solution promoted the photoreduction reaction at the maximum rate happened. The photoreduction mechanism of Cyt c was intramolecular electron transfer, including the formation of porphyrin cation radical as an active intermediate excited by 280 nm light. In addition, results of fluorescence and CD spectra indicated that the protein-peptide chain structure, while the secondary structure of the protein changes, α-helix content decreased, β-sheet content increased.However, the secondary structure of Cyt b5 is still dominated by α-helix in the photoreduction process. Moreover, it provides a theoretical basis for the redox reaction and electron transfer mechanism in life.