Time-resolved fluorescence analysis of photosystem II core antennas CP43 and CP47 from spinach

Abstract

Light-harvesting antenna complex LHCII absorbs solar energy and transfer it to the PSII reaction center passes through core antennas CP43 and CP47, respectively. These two components, which binds only Chl a and b -Car and no Chl b is present, were purified from spinach and their pigment content were confirmed by HPLC. The mechanism of energy transfer between carotenoid and chlorophyll has not been identified in these core antennas. The purified CP43 and CP47 were used to measure steady-state chlorophyll fluorescence spectra and fluorescence decay kinetics. Their time-resolved dynamic fluorescence spectra were obtained by selectively excited at 514 nm. It was found that a peak locates about 683 nm and its lifetime equals 3.55 ns in CP43. As for CP47, the emission spectra form 650 to 780 nm revealed a peak at 692 nm and its fluorescence lifetime was determined as 3.25 ns. The energy transfer constants form b -Car to Chl a in CP43 and CP47 are 9.6 ´ 1011s-1 and 1.3 ´ 1012s-1, and the energy transfer efficiencies are 66.5% and 76.2%, respectively. According to the Foster resonance mechanism, the edge-to-edge distances between b -Car to Chl a in CP43 and CP47 were calculated to be averagely equals 0.11 nm and 0.08 nm. Our other work revealed the existence of two groups of Chl a in both CP43 and CP47. The excitation energy transfer mechanism between these two different groups of Chl a are going along by picosecond fluorescence and femtosecond difference absorbance spectra