Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.3.5.1 (succinate dehydrogenase)
 8,177 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Laser flash-induced changes of the fluorescence yield were studied in aggregates of light-harvesting complex II (LHCII) on a time scale ranging from microseconds to seconds. Carotenoid (Car) and chlorophyll (Chl) triplet states, decaying with lifetimes of several microseconds and hundreds of microseconds, respectively, are responsible for initial light-induced fluorescence quenching via singlet-triplet annihilation. In addition, at times ranging from milliseconds to seconds, a slow decay of the light-induced fluorescence quenching can be observed, indicating the presence of additional quenchers generated by the laser. The generation of the quenchers is found to be sensitive to the presence of oxygen. It is proposed that long-lived fluorescence quenchers can be generated from Chl triplets that are not transferred to Car molecules. The quenchers could be Chl cations or other radicals that are produced directly from Chl triplets or via Chl triplet-sensitized singlet oxygen. Decay of the quenchers takes place on a millisecond to second time scale. The decay is slowed by a few orders of magnitude at 77 K indicating that structural changes or migration-limited processes are involved in the recovery. Fluorescence quenching is not observed for trimers, which is explained by a reduction of the quenching domain size compared to that of aggregates. This type of fluorescence quenching can operate under very high light intensities when Chl triplets start to accumulate in the light-harvesting antenna.
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PMID:Generation of fluorescence quenchers from the triplet states of chlorophylls in the major light-harvesting complex II from green plants. 1095 37

Carotenoid excited-state properties are characterized and compared in reaction centers (RCs) of wild-type (WT) Rhodobacter (Rb.) sphaeroides , and a mutant VR(L157), in which the near-infrared absorbance band associated with the primary electron donor, P, is missing. Energy transfer from the carotenoid (spheroidenone) S(2) and relaxed S(1) excited states to an adjacent monomeric-bacteriochlorophyll is unchanged between WT and the mutant RC samples. However, two other excited states, including a vibrationally hot S(1) state and a state referred to as S*, have distinct properties in the two RCs. The lifetime of the hot S(1) state is significantly shortened in the P-less mutant compared to WT RCs (450 fs vs 800 fs, respectively), and there is a nearly 2-fold decrease in the efficiency of energy transfer from the carotenoid to bacteriochlorophyll in the P-less mutant relative to WT RCs. The fact that both the observed hot S(1) excited state lifetime and the energy transfer efficiency decrease in the mutant implies that the intrinsic lifetime of the hot S(1) state in the P-less mutant has decreased. Interestingly, the S* state is observed only in the P-less mutant, and it is not present in the WT. The change in the hot S(1) lifetime between WT and mutant RCs, and the formation of the S* state only in the mutant, suggests that the carotenoid binding pocket in the P-less mutant is substantially altered. The excited-state behavior of spheroidene in WT RCs isolated from anaerobically grown cells was also characterized and compared with previous studies of spheroidene in the light-harvesting complex II (LH2) from Rb. sphaeroides . Differences in the photophysical properties of spheroidene between WT RCs and LH2 parallel those observed for spheroidenone between WT and VR(L157) mutant RCs. On the basis of the structural information available for both RCs and LH2, it appears that the hot S(1) state and the S* state are sensitive to the structural constraints imposed by protein-carotenoid interactions. Finally, in the VR(L157) mutant, it is possible to directly observe the carotenoid triplet state, likely formed via quenching of the bacteriochlorophyll triplet state. This provides direct experimental evidence for triplet energy transfer to the carotenoid, a process that is integral to the photoprotective role of carotenoids in bacterial RCs.
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PMID:Carotenoid excited-state properties in photosynthetic purple bacterial reaction centers: effects of the protein environment. 2148 46