Spectral Distributions of “Trap” Pigments in the RC, CP47, and CP47−RC Complexes of Photosystem II at Low Temperature: A Fluorescence Line-Narrowing and Hole-Burning Study

Abstract

Broad-band absorption and fluorescence, fluorescence line-narrowing (FLN), and spectral hole-burning experiments have been performed on the Qy-band of three subcore reaction-center complexes of photosystem II between 1.2 and 4.2 K: the isolated reaction center (RC), the inner core antenna CP47, and the CP47−RC complex. In the RC, fluorescence line-narrowing (FLN) is observed for excitation wavelengths λexc ≥ 676 nm, whereas in CP47, this occurs for λexc ≥ 680 nm. The FLN spectra of CP47−RC appear to be the sum of the individual spectra of the RC and CP47, an indication that this complex has two “traps”. This has been confirmed from the spectral distributions obtained by measuring the hole depth (at constant hole width) as a function of λexc, as previously done for the RC [Groot, M. L., et al. J. Phys. Chem. 100, 1996, 11488]. The maxima of these distributions are at ∼682 nm for the RC “trap” and at ∼690 nm for the CP47 “trap” within the CP47−RC complex. Further support that the two distributions of pigments in CP47−RC belong indeed to “trap” pigments is provided by the “effective” homogeneous line width Γ‘hom determined as a function of temperature for various excitation and detection wavelengths.