The protein secondary structure and pigments' microenvironment in photosystem 1 (PS1) complexes were studied in the temperature range of 25-80 °C using Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy, respectively. Quantitative analysis of the component bands of the amide I band (1 700-1 600 cm-1) showed no significant change below 50 °C. However, apparent conformational changes occurred at 60 °C and further continued at 70 and 80 °C accompanied with transitions of secondary structure mainly from α-helix to the β-sheet structures. CD analysis demonstrated that the regular arrangement, viz. protein microenvironment of pigments of PS1 complexes, was destroyed by heat treatment which might come from the changes of protein secondary structure of PS1. The CD signals at 645 nm contributed by chlorophyll (Chl) b of light-harvesting complex 1 (LHC1) were easily destroyed at the beginning of heat treatment (25-60 °C). When temperature reached 70 and 80 °C, the CD signals at 478 nm contributed mainly by Chl b of LHC1 and 498 nm contributed by carotenoids decreased most rapidly, indicating that LHC1 was more sensitive to high temperature than core complexes. In addition, the oxygen uptake rate decreased by 90.81 % at 70 °C and was lost completely at 80 °C showing that heat treatment damaged the regular function of PS1 complexes. This may be attributed to heat-induced changes of pigment microenvironment and protein secondary structure, especially transmembrane α-helix located in PsaA/B of PS1. and Z.-H. Hu ... [et al.].
Energy transfer of aromatic amino acids in photosystem 2 (PS2) core antenna complexes CP43 and CP47 was studied using absorption spectroscopy, fluorescence spectroscopy, and the 0.35 nm crystal structure of PS2 core complex. The energy of tyrosines (Tyrs) was not effectively transferred to tryptophans (Trps) in CP43 and CP47. The fluorescence emission spectrum of CP43 and CP47 by excitation at 280 nm should be a superposition of the Tyr and Trp fluorescence emission spectra. The aromatic amino acids in CP43 and CP47 could transfer their energy to chlorophyll (Chl) a molecules by the Dexter mechanism and the Föster mechanism, and the energy transfer efficiency in CP47 was much higher than that in CP43. In CP47 the Föster mechanism must be the dominant energy transfer mechanism between aromatic amino acids and Chl a molecules, whereas in CP43 the Dexter mechanism must be the dominant one. Hence solar ultraviolet radiation brings not only damages but also benefits to plants. and Y. G. Qu .... [et al.].
The structural characteristics of the extra-membrane domains and guanidine hydrochloride-induced denaturation of photosystem 2 (PS2) core antenna complexes CP43 and CP47 were investigated using fluorescence emission and circular dichroism (CD) spectra. The extra-membrane domains of CP43 and CP47 possessed a certain degree of secondary and tertiary structure and not a complete random coil conformation. The tertiary structure and the chlorophyll (Chl) a microenvironment of CP47 were more sensitive to guanidine hydrochloride (GuHCl) than that of CP43. Changes in energy transfer from β-carotene to Chl a corresponded well to changes in the tertiary structure while their correlation with changes in the secondary structure was rather poor. Unlike most of water-soluble proteins, both CP43 and CP47 are partly resistant to denaturation induced by guanidine hydrochloride (GuHCl); the denaturation of CP43 or CP47 is not a two-state process. Those features most probably reflect their character as intrinsic membrane proteins. and Y.-G. Qu ... [et al.].