Characterization And Energy Transfer Of Chlorophyll-protein Complexes Of Chroomonas Placoidea

The absorption and fluorescence spectral characteristics at room temperatureand77K of intact cells and thylokoids of Chroomonas placoidea, which arecultured by our laboratory, are determined and analyzed. It is proposed that aportion of phycocyanin （PC） in intact cells is in a free state, and can bedynamically combined with thylakoids; It is also found that the excited energyabsorbed by Chl a and Chl c tend to transfer to PSⅡor short wavelength of Chl a,while light energy absorbed by PC is assigned to both two photosystems, andcontribute mainly to fluorescence emitted by long wavelength of Chl a; There isno730nm long wavelength of fluorescence, which is designated as characteisticfluorescence of PSⅠin higher plants, are observed in77K fluorescence spectra ofintact cell, thylakoid membrane, PSⅠcore complex and PSⅠparticles. This resultshows that the cryptophytic algae is distinct from higher plants in both structureand in energy transfer of PSⅠ.By using the method of sucrose density gradient centrifugation, five activechlorophyll-protein complexes and nine sub-complexes were separated fromthylakoids, including one large molecular weight of PSⅠcore complexes, which isnever reported before. The absorption spectra, fluorescence spectra at roomtemperature and77K, as well as polypeptide composition of chlorophyll-proteincomplexes and its sub-complexes are measured and studied systematically.Circular dichroism is also employed to give a band (190~750nm) of spectra ofthree isolated chlorophyll-protein complexes. The results show that:①In the farUV region（190~250nm）, the proportion of random coil in each complex is similar,which accounts for about30%according to secondary structure prediction; Thereis a high proportion of α-helix and β-turn in PS Ⅰ particle than in PS Ⅱparticle andlight harvesting complex, but there is hardly any β-sheet.②In the near UV region（250~340nm）, no signal peak of Tyr is observed in all the complexes in tertiarystructure of aromatic amino acids.③In the visible light region（400~750nm）,whether there is a signal peak constitutes a distinction between light harvestingcomplexes and core complexes in cryptophytic alga. These results not only give new information of the characteristics of chlorophyll protein complexes fromcryptophytic alga, but also provide a new foundation for the analysis andidentification of chlorophyll protein complexes.