Picosecond Fluorescence Studies of P700‐enriched Particles of Spinach Chloroplasts

Abstract

Dynamic properties of the picosecond fluorescence of highly enriched reaction-center particles of photosystem I (8 -10 chlorophylls/P700) prepared from spinach have been investigated. The number ( N ) of photons used to excite chlorophyll molecules per reaction center was controlled between 0.06 and 80. The lie lifetime was ca. 25 ps for N 5 1. which is much shorter than previously measured lifetimes of photosystem I particles. The initial fluorescence intensity saturated at higher excitation intensities ( N 2 1). This was interpreted in terms of interaction and annihilation among excited chlorophyll molecules which occur almost entirely within the duration of a laser flash. The spectrum-resolved fluorescence decay was faster at 690 than at 680 nm. This implies that two kinds of antenna chlorophylls. apart from and in close proximity to P700, have different lifetimes. Upon heat treatment a component with a much longer fluorescence decay time was observed. The growth of this component upon heat treatment at increasing temperatures showed a correlation with a decrease in the amount of P700 that could be photooxidized.

Primary photochemistry in photosystem-I

“…Thus the lifetime of the radical pair (in the order of 10 ns), measured opticaily under these conditions [108], probably reflects P700+Ao recombination. This agrees with the lifetime of a phase of fluorescence (6 ns) measured under similar conditions and which has been attributed to recombination luminescence [56]. This lifetime is also remarkably similar to that of the primary radical pair, P870 + BPh-, in the bacterial reaction center [90].…”

Electronic excitation transport in photosynthesis and crystal and molecular structures of porphyrin compounds

“…. 4.1) are clustered around 200 to 250 ps; these are similar to the "Intermediate" fluorescence components characterized in PS I preparations withChi a/P700 ratios greater than 65[8,40,41]. This decay component was not observed in our PS 1-60 pump-probe experiments[31].…”

Theory of Picosecond-Laser-Induced Fluorescence from Highly Excited Complexes with Small Numbers of Chromophores

“…By observing the kind of effect described in Fig. 3, Kamogawa et al (18) have deduced that annihilation occurs almost entirely during the pulse in small PSI particles (8-10 Chls/RC).…”

“…Some quantum yield and single-pulse, picosecond timeresolved fluorescence measurements on small complexes (consisting of N = 2, 3, .... 10 chromophores) extracted from systems of general interest to photosynthesis have been carried out by several researchers (17)(18)(19)(20)(21)(22). However, the experimental answer to the question of the existence, and, if it exists, the rate of the annihilation process in a fairly small system is not complete.…”