Physical And Chemical Factors Of Ps Ii Inner Antenna Cp43 And Cp47 Pigment-protein Complex Structure And Function

CP43 and CP47, the core antenna of PSII, were isolated and purified from spinach chloroplast. The effects of physical and chemical factors, such as acid , alkali . strong light and high temperature, on their structure and function were investigated by the spectra techniques (such as absorption spectra, flourescence spectra and CD spectra) and biochemical methods (such as HPLC and electrophoresis). The results as follow:1.The effects of acid and alkali on the structure and function of CP43 and CP471 ) , Both acid and alkali treatments caused drop of the absorption peak in red and blue region, increase of absorption of satellite band of Soret band and blue shift of the absorption peaks of CP43 and CP47. Both CP43 and CP47 presented the absorption peaks of Pheophytin a at 510 and 542 nm under acid condition, while alkali treatment caused a new absorption peak at 642 nm. The changes of the absorption spectra were attributed to the interaction of bound pigments with H~+ or OH~-. Under acid conditions, Chl a changes into Pheo a, CP43 and CP47 were etiolated, but Pheo a still bound strongly to, other than dissociated from, the apoprotein even in the process of mild (un-denature) PAGE. Under alkali conditions, although most pigments were also bound to apoprotein, they had a weakened affinity with it, and dissociated fromapoprotein when mild PAGE was carried out. The 642 nm peak that occurred under alkali is from the interaction of OH- with Chl a. It need the change of the protein's secondary structure. The action should not occur if the structure of protein remains unchanged, or Chl a molecule surrounded by urea molecules. The appearance of the 642 nm absorption peak, and the dissociation of pigment from the apoprotein in the process of mild PAGE, depend on the relative amount of OH" to the Chl a.2), The energy transfer between β-Car and Chl a in CP43 was easily disturbed by alkali, while that of CP47 was readily affected by acid. As to the effects on the secondary structure of proteins in CP43 and CP47, acid was far less than alkali. Both acid and alkali disturbed the micro-environment of Chl a and interfered exciton interaction between Chl a molecules.3), Acid and alkali affect the light absorption, energy transfer and protein secondary of CP43 and CP47 in different way. H+ can permeate into the internal space of CP43 and CP47, change Chl a into Pheo a and disturb the micro-environment of pigments without damaging the secondary structure of protein. While OH" can induce the protein unfolding at first, then saponifies Chl a to cholophyllide a and disturbs the micro-environment of pigments.4), Both acid or alkali treatment caused changes of the elution time and elution area of Chl a in CP43 and CP47, in the process of HPLC, while that of β-Carwas little affected. It indicated that the Car was little damaged by acid or alkali.2. The effects of strong light on the structure and function of CP43 and CP47Strong light (1000 mol E./m2.s) was found to bring about considerable bleaching of chlorophyll a and degradation of protein, but they were inhibited obviously by sodium thiosulfate. Under same condation, the Car was little affected.3. The effects of high temperature on the degradation of CP43x CP47 and other subunits of PSIIPSII OECC , RC-CP47 , RC CP43 and CP47 pigment complexes from spinach chloroplasts were isolated and purified. The difference of heat-induced degradation of PSII subunits in these complexes was investigated. It was showed that the heat-sensitivity of subunits of PSII was different distinctly: CP43, D2, CP29, LHCII > D1 CP47 >> PsbO, PsbP, PsbQ and Cytb559 ( subunit).