Spectroscopic Study On Interaction Between The Heavy Metals And The 23 KD å'Œ 17 KD Extrinsic Proteins Of Photosystem â…¡ From Spinach

The oxygen-evoluting photosystem II (PSII) complex of higher plants contains three extrinsic proteins of 33, 23 å’Œ 17 kD, which encoded by PsbO, PsbP and PsbQ genes, these proteis are essential for the stability and full activity of the oxygen-evoluting complex. The 17 kD protein has been observed to increase the binding affinity of Cl^- to PSII and the 23 kD protein to be involved increasing the binding affinities of both Cl^- and Ca²⁺.The aims of this study are to investigate the interaction between heavy metals and extrinsic polypeptides 23 kD and 17 kD of PSII in spinach and prepare the antiserum of extrinsic polypeptides.In the first part, we analyzed the conformational changes of 23 kD protein induced by binding of metal ions through fluorescence spectra and ultraviolet differential spectra.Under different pH values (2.0-10.0), the interaction of metal ions with 23 kD protein was very different as reflected by distinct spectral characteristics. The main results as follows:(1) The intrinsic fluorescence of the protein was quenched by Hg²⁺ and Mn²⁺ in all pH conditions (pH 2.0-pH 10.0), and the maximum fluorescence emission was slightly influenced by binding of metal ions, which is indicative of slight effect on the microenvironment of aromatic amino acid residues of metal ions. (2) Distinguished...