Raman spectra of purified oxygen evolution core complexes (Pd OECC) thin films on silver mirror substrates have been taken over the frequency range of 250-3100 cm -1 by surface enhanced Raman scattering (SERS). Besides the fundamental frequency modes of β_carotene in Pd OECC, many weak peaks are observed. According to the selection rules of overtone and combination bands, most of them are attributed to the second_order Raman spectra of β_carotene. Compared with the SERS of normal Pd OECC, the SERS of Pd OECC after strong illumination shows a decrease in scattering intensity and an increase in line widths, indicating changes of conformation and micro_environment of β_carotene. The results of SERS are consistent with the changes of absorption spectrum of Pd OECC induced by strong illumination. There are no changes that can be ascribed to new vibration bands, so it is deduced that Pd OECC on the silver mirror is identical to that in the solution. In summary, SERS proved a good method to study the photodamage mechanism of photosynthesis.
Linear dichroism (LD) spectroscopy is an important technique in the study of the orientation and organization of pigments in the photosynthetic membrane complexes in vivo and in vitro . In this work, the orientation of the pigments in the isolated photosystem Ⅱ (PSⅡ) sub_core reaction center complexes was analyzed and characterized by means of low temperature absorption and LD spectroscopy. The preparations containing different amounts of CP47 isolated from spinach (Spinacia oleracea L.) chloroplast were used in order to investigate the orientation of pigments in the PSⅡ sub_core CP47/D1/D2/Cyt b_559 (CP47/D1/D2) complexes. Chlorophyll a (Chl a) absorbing at 680 nm in CP47/D1/D2/Cyt b_559 complex showed an orientation of the Q y transition parallel to the membrane plane. It is proposed that there are two forms of β_carotene (β_Car) in CP47/D1/D2/Cyt b_559 complex, denoted as β_Car (Ⅰ) and β_Car (Ⅱ), with different orientations, β_Car (Ⅰ) at 470 and 505 nm is roughly parallel to the membrane plane, and β_Car (Ⅱ) at 460 and 490 nm seems to be perpendicular orientation. Upon the photoinhibitory experiment β_Car (Ⅱ) was found to be photosensitive and easily photodamaged. It also showed that the positive LD signal observed at 680 nm was quite complicated. This signal is tentatively attributed to P680 and some Chl a of antenna in CP47 protein based upon our measurements.
The structural and functional alterations within the PSⅡ membrane from phosphatidylcholine reconstitution and Triton X_100 (TX_100) treatment were studied by using Fourier transform_infrared (FT_IR) spectroscopic technique and oxygen electrode. Phosphatidylcholine reconstitution showed no significant effect on the protein secondary structures of PSⅡ membrane but an increase of the rate of PSⅡ_mediated oxygen_evolution. The phosphatidylcholine lipids with different length of acyl chains displayed different capabilities to stimulate oxygen_evolution. In contrast, perturbation of the bilayer lipids by TX_100 resulted in obvious changes of the protein secondary structures within the PSⅡ membrane and in the loss of the PSⅡ_mediated oxygen_evolving activity. The results indicate the importance of membrane integrity in maintaining the stability of the photosynthetic membrane proteins.
