Hydration effect on electron transfer in cytochrome c monitored by μSR

The μSR measurements of oxidized form of cytochrome c of horse heart were carried out at RIKEN-RAL and at J-PARC MUSE. Cytochrome c is one of the members of respiratory chain in mitochondria. The muon spin time relaxation spectra of the samples wetted with H₂O and D₂O, whose water contents were approximately 20 wt.%, were fitted using Risch–Kehr (R–K) function. The longitudinal relaxation parameter (Γ) showed an inverse dependence on B_ext, in the region from 1000 to 3950 G at room temperature and the region from 200 to 3950 G below 200 K, and it was suggested by the R–K theory that muon spin relaxation due to the one-dimensional electron movement would be dominant below 200 K. The difference in the spectra of the samples wetted with H₂O and D₂O was small and it was concluded that muon stopped on cytochrome c and we monitored the behaviors of the electron brought in by μ⁺ in cytochrome c through the relaxation process of the μ⁺. (author)