Ultrafast Primary Processes in Photosystem I of the Cyanobacterium Synechocystis sp. PCC 6803

• Published in: Biophysical journal Vol. 76; no. 6; pp. 3278 - 3288
• Main Authors: Savikhin, Sergei, Xu, Wu, Soukoulis, Victor, Chitnis, Parag R., Struve, Walter S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-06-1999; Biophysical Society
• Subjects: Anisotropy; Bacteria; Biophysical Phenomena; Biophysics; Chlorophyll; Chlorophyll - chemistry; Chlorophyll - metabolism; Chlorophyll - radiation effects; Cyanobacteria - metabolism; Cyanobacteria - radiation effects; Cyanophyta; electron transfer; Equilibrium; Flowers & plants; Fluorescence; Kinetics; Models, Biological; Photochemistry; Photosynthesis; Photosynthetic Reaction Center Complex Proteins - chemistry; Photosynthetic Reaction Center Complex Proteins - metabolism; Photosynthetic Reaction Center Complex Proteins - radiation effects; Protein Conformation; Synechocystis; OPA; ESA; PB; P700; SE; Chl; DAS; PS I
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(99)77480-1

Ultrafast primary processes in the trimeric photosystem I core antenna-reaction center complex of the cyanobacterium
Synechocystis sp. PCC 6803 have been examined in pump-probe experiments with ∼100
fs resolution. A global analysis of two-color profiles, excited at 660
nm and probed at 5
nm intervals from 650 to 730
nm, reveals 430
fs kinetics for spectral equilibration among bulk antenna chlorophylls. At least two lifetime components (2.0 and 6.5
ps in our analysis) are required to describe equilibration of bulk chlorophylls with far red-absorbing chlorophylls (>700
nm). Trapping at P700 occurs with 24-ps kinetics. The multiphasic bulk ↔ red equilibration kinetics are intriguing, because prior steady-state spectral studies have suggested that the core antenna in
Synechocystis sp. contains only one red-absorbing chlorophyll species (C708). The disperse kinetics may arise from inhomogeneous broadening in C708. The one-color optical anisotropy at 680
nm (near the red edge of the bulk antenna) decays with 590
fs kinetics; the corresponding anisotropy at 710
nm shows ∼3.1
ps kinetics. The latter may signal equilibration among symmetry-equivalent red chlorophylls, bound to different monomers within trimeric photosystem I.