Charge-Transfer Dynamics in Plastocyanin, a Blue Copper Protein, from Resonance Raman Intensities

Abstract

The resonance Raman intensities for parsley plastocyanin, a blue copper protein involved in electron transport in plant photosynthesis, have been measured at wavelengths throughout the S(Cys) → Cu charge-transfer absorption band centered at 597 nm in an effort to determine the structural and dynamic role of inner- and outer-sphere reorganization in the kinetics of charge transfer. Self-consistent analysis of the absorption band and the resulting resonance Raman excitation profiles demonstrates that the charge-transfer absorption band is primarily homogeneously broadened. The homogeneous line width is composed of population decay and solvent-induced dephasing. The excited-state lifetime of 20 ± 15 fs calculated here from the observed fluorescence suggests that the charge-transfer state decays rapidly via lower-lying ligand-field states. The spectral line shape dictates that this population decay be modeled as a Gaussian of line width 230 cm-1. The reorganization energy obtained from the resonance Raman int...