Effect of Ce3+ on spectral characteristic of D1/D2/Cytb559 complex from spinach

It was studied by spectroscopy that PSII reaction center complex consisting of three polypeptides, D1, D2 and Cytb559, were purified from PSII particle of CeCl3 treated spinach. The results of the experiment show that Ce3+ could improve the growth of spinach, and accelerate electron transport of PSII particles. Of chl-a of UV-Vis spectrum of D1/D2/Cytb559 complex, Soret band was blue-shifted by 3 nm and Q band by 2 nm, respectively, and the fluorescence emission peak was blue-shifted by 5 nm in CeCl3-treated spinach compared with the one in control. By the extended X-ray absorption fine structure (EXAFS) spectroscopy methods, it has been found that Ce3+ is coordinated with 8 nitrogen atoms in the first coordination shell with Ce-N bond length of 0.253 nm, and Ce3+ with 6 oxygen atoms in the second coordination shell with Ce-O bond length of 0.32 nm. However, the secondary structure of D1/D2/Cytb559 complex by circular dichroism (CD) spectroscopy has no significant change after CeCl3 treated. It might be that Ce3+ binds to porphyrin rings of chlorophyll and oxygen of amino acid residue of polypeptide in D1/D2/Cytb559 complex, and then accelerates the primary reaction of PSII, intensifies function of P680+ primary electron donor of D1/D2/Cytb559, but there is little change in conformation of PSII reaction center complex.