期刊
EUROPEAN JOURNAL OF BIOCHEMISTRY
卷 268, 期 2, 页码 260-267出版社
BLACKWELL SCIENCE LTD
DOI: 10.1046/j.1432-1033.2001.01874.x
关键词
fluorescence quenching; light-harvesting complex; photoprotection; xanthophylls
Nonradiative dissipation of excitation energy is the major photoprotective mechanism in plants. The formation of zeaxanthin in the antenna of photosystem II has been shown to correlate with the onset of nonphotochemical quenching in vivo. We have used recombinant CP29 protein, over-expressed in Escherichia coli and refolded in vitro with purified pigments, to obtain a protein indistinguishable from the native complex extracted from thylakoids, binding either violaxanthin or zeaxanthin together with lutein. These recombinant proteins and the native CP29 were used to measure steady-state chlorophyll fluorescence emission and fluorescence decay kinetics. We found that the presence of zeaxanthin bound to CP29 induces a approximate to 35% decrease in fluorescence yield with respect to the control proteins (the native and zeaxanthin-free reconstituted proteins). Fluorescence decay kinetics showed that four components are always present but lifetimes (tau) as well as relative fluorescence quantum yields (rfqy) of the two long-lived components (tau (3) and tau (4)) are modified by the presence of zeaxanthin. The most relevant changes are observed in the rfqy of tau3 and in the average lifetime (approximate to 2.4 ns with zeaxanthin and 3.2-3.4 ns in the control proteins). When studied in vitro, no significant effect of acidic pH (5.2-5.3) is observed on chlorophyll a fluorescence yield or kinetics. The data presented show that recombinant CP29 is able to bind zeaxanthin and this protein-bound zeaxanthin induces a significant quenching effect.
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