Fluorescence excitation spectra of different protochlorophyll(ide) (PChlide) a forms in intact etiolated cucumber cotyledons showed a pronounced increase in intensity of the 390 nm band in comparison with spectra of the pigment in Solutions. The native PChlide F657 also had an additional band at 360 nm in its excitation spectra, which disappeared after leaf homogenization and was restored by addition of dithionite. The restoration correlated with changes around 340 nm in the excitation spectrum of blue-green fluorescence. In consideration of this fact, the 360 nm band seems to correspond to energy transfer from NADPH to PChlide a. After the onset of irradiation a new band appeared at 380 nm in the excitation spectrum of the main pigment fluorescence, which was very similar to that found in the absorption spectinm of isolated Chl a. Moreover, in the Soret region the excitation spectrum had a double band splitting which disappeared only after the Shibata shift, simultaneously with the disappearance of the 360 nm band. Besides the well-known PChl(ide) F633, F642, and F657 forms, etiolated cucumber cotyledons háve emission at 673 nm. Its excitation spectrum was hardly distinguishable from the PChlide F657 fluorescence excitation spectrum in etiolated samples. In the irradiated plants this band had excitation spectrum of monomeric Chl a. The intensity of band at 673 run decreased and transiently increased after PChlide photoconversion. The dynamics of these fluorescence intensity changes under inadiation showed positive correlation both with PChlide F657 and with PChl(ide) F642, indicating the short wavelength Chl a preexistence in etiolated plants and its additional formation after the onset of irradiation.
Spectroscopy was used to investigate the fluorescence quenching mechanism in light-harvesting complex 2 (LHC2). The 77 K fluorescence excitation spectroscopy was performed for detection of aggregation state of LHC2 treated with different concentrations of octylphenol poly(ethyleneglycol ether)10 (TX-100). Resonance Raman (RR) spectra excited with 488, 496, and 514 nm provided molecular configuration of neoxanthin, lutein 1, and lutein 2, respectively. At increased concentration of TX-100, the RR signals of xanthophylls were enhanced in the four frequency regions, which was accompanied with increase of fluorescence of chlorophyll (Chl) a. Thus the absorption of the three xanthophyll molecules was inclined to excitation wavelength, which proved that functional configurations of xanthophyll molecules in LHC2 were vital for fast transfer of excitation energy to Chl a molecules. Changes in the v4 region (C-H out-of-plane bending modes, at ∼960 cm-1 in RR spectra) demonstrated that the twist feature of neoxanthin, lutein 1, and lutein 2 molecules existed in LHC2 trimers, however, it was lost in the LHC2 macro-aggregates. In the second derivative absorption spectra of LHC2, neoxanthin absorption was not detected in LHC2 macro-aggregates, while evident absorption was found in LHC2 trimers and this absorption decreased obviously when TX-100 concentration was higher than 1 mM. Hence the neoxanthin molecule had a structural role in formation of LHC2 trimers. The RR and absorption spectra also implied that carotenoid molecules constructed the functional LHC2 trimers via their intrinsic configuration features, which enabled energy transfer to Chl a efficiently and led to lower fluorescence quenching efficiency. In contrast, these intrinsic twist configurations were lost in LHC2 macro-aggregates and led to lower energy transfer efficiency and higher fluorescence quenching efficiency. and Z. H. Hu, F. Zhou, C. H. Yang.
The activities of photosystem 2 (PS2) and whole chain electron transport declined in high temperature treated cells at the room temperature beyond 35 °C, while photosystem 1 (PS1) showed increased activity. Thylakoid membrane studies did not exhibit increase in PS1 activity indicating that the enhancement of PS1 activity is due to permeability change of cell membranes. However, the electron transport activity measured from reduced duroquinone to methylviologen which involves intersystem electron transport was extremely sensitive to high temperature. The activity of PS2 at different irradiance, which was accompanied by alterations in absorption and fluorescence emission properties, indicated changes in the energy transfer processes within phycobilisomes. Thus high temperature has multiple target sites in photosynthetic electron transport system of Spirulina platensis. and V. Venkataramanaiah, P. Sudhir, S. D. S. Murthy.
The model conjugates phycocyanin-allophycocyanin (C-PC-APC) and phycoerythrocyanin-phycocyanin-allophycocyanin (PEC-C-PC-APC) were synthesized by using a heterobifunctional coupling reagent N-succinimidyl-3-(2-pyridyldithio)propionate. The rod-core complex (αβ)6 PCLRC 27(αβ)3 APCLC 8.9 and phycobilisomes were separated from Anabaena variabilis. Energy transfer features for the conjugates and the complexes were compared. The absorption and fluorescence emission spectra indicated that the linker-peptides mediate interaction of phycobiliproteins and prompt energy transfer. The energy transfer in the conjugates was detected by fluorescence emission spectra and confirmed by the addition of dithiothreitol. The conjugates may be used as models for studying the energy transfer mechanism in phycobilisomes. and Jiquan Zhao ... [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.].