Initial electron donor and acceptor in isolated Photosystem II reaction centers identified with femtosecond mid-IR spectroscopy

• Published in: Proceedings of the National Academy of Sciences - PNAS 2005-09, Vol.102 (37), p.13087-13092
• Main Authors: Groot, M.L, Pawlowicz, N.P, Wilderen, L.J.G.W. van, Breton, J, Stokkum, I.H.M. van, Grondelle, R. van
• Format: Article
• Language: English
• Subjects: Absorption spectra; Bacteria; Biochemistry; Biological Sciences; Charge separation; Chlorophyll; Chlorophyll - metabolism; electron transfer; Electron transfer reactions; Electron Transport; Electrons; esters; Excitons; Flowers & plants; Infrared spectroscopy; Kinetics; Molecules; Oxidation-Reduction; pheophytin; Pheophytins - metabolism; Photosynthesis; photosynthetic reaction centers; photosystem II; Photosystem II Protein Complex - chemistry; Photosystem II Protein Complex - metabolism; Pigments; Plant Proteins - chemistry; Plant Proteins - metabolism; Spectral bands; Spectrophotometry, Infrared - instrumentation; Spectrophotometry, Infrared - methods; Spectroscopic analysis; Spectrum analysis; spinach; Spinacia oleracea; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0503483102

Despite the apparent similarity between the plant Photosystem II reaction center (RC) and its purple bacterial counterpart, we show in this work that the mechanism of charge separation is very different for the two photosynthetic RCs. By using femtosecond visible-pump-mid-infrared probe spectroscopy in the region of the chlorophyll ester and keto modes, between 1,775 and 1,585 cm-1, with 150-fs time resolution, we show that the reduction of pheophytin occurs on a 0.6- to 0.8-ps time scale, whereas P+, the precursor state for water oxidation, is formed after approximately equal to 6 ps. We conclude therefore that in the Photosystem II RC the primary charge separation occurs between the "accessory chlorophyll" ChlD1 and the pheophytin on the so-called active branch.