THE EFFECT OF CU(II) IONS BOUND WITH TRIDENTATE SCHIFF-BASE LIGANDS UPON THE PHOTOSYNTHETIC APPARATUS

The effect of (N-pyruvidene-beta-alaninato)copper(II)monohydrate (Cu(p yr-beta-ala)) on the photosynthetic apparatus of spinach chloroplasts was investigated. It was found that Cu(pyr-beta-ala) inhibits the phot osynthetic electron transport in chloroplasts due to its interaction w ith the photosynthetic centers. Its sires of action have been determin ed to be not only the intermediate Tyr(Z)(.) (reported by Schroder et al., 1994), but also the intermediate Tyr(D)(.), which are situated in D-1 and D-2 proteins on the donor side of PS 2. The interaction of Cu (pyr-beta-ala) with these intermediates was manifested by a decrease o f the intensity of EPR signals IIslow and IIvery fast, respectively, i n chloroplasts treated with Cu(pyr-beta-ala). The appearance of lines corresponding to Mn2+ ions in EPR spectrum of Cu(pyr-beta-ala)-treated chloroplasts and simultaneous disappearance of the manganese band in spectra of band radionuclide X-ray fluorescence analysis (RFA) confirm that a further site of Cu(pyr-beta-ala) action is the manganese clust er in the oxygen evolving complex (OEC) on the donor side of PS 2. One of the suggested mechanisms of action of Cu(pyr-beta-ala), namely che latation of its copper(II) ions with tryptophan and tyrosine constitue nts of proteins situated in photosynthetic centres, has been confirmed by the results of fluorescence studies (quenching of the emission ban ds of the above mentioned aromatic amino acids in the presence of Cu(p yr-beta-ala)) and EPR spectroscopy (differences in the form of spectra of Cu2+ ions corresponding to the dissolved Cu(pyr-beta-ala) and to c hloroplast-trapped Cu2+ ions of this compound). The second suggested m echanism of action of Cu(pyr-beta-ala) is the substitution of manganes e and calcium ions present in OEC by copper, which was confirmed by th e intensity decrease of their bands (channel numbers: 91, 106 for Mn a nd 39 for Ca) in RFA spectra of Cu(pyr-beta-ala)-treated chloroplasts and simultaneous increase of the intensity of corresponding bands belo nging to Cu (channel numbers: 146, 168).