Eleonora Trif and Vasile V. Trif
Australian Group of Photosynthesis, Centr. Physiology & Biochemistry of Vegetables, Tarlee 5411, S. Australia.
It is well know the presence in the quantasomes from chloroplast tylakoid of two-copper complexes with the molecular weight of 218. Migration of Cu(II) ions, their complexation and activity are essential in understanding the photosynthetic event. Cu(II) - species formed in leaves of plants kept in solutions containing excess of ions (0.0125 - 0.5%) were investigated by UV-VIS and EPR spectroscopies. After 3-5 days of nutrition with solutions containing Cu(II) in concentrations lower than 0.05%, immobile Cu(II) - species are accumulated around the border area of the leaves, achieving the first step in necrosis. The EPR parameters (gII = 2.24, g = 2.05, AII - 18.5mT, A = 2.8mT), for the pigment extracted from these leaves, are typical for an axial symmetry of the ligand field, Fig 1. The ligand superhyperfine structure, with a0 = 1.41mT, confirms the accommodation of Cu(II) in the porphyrine ring, being coupled equally to the four pyrole nitrogens and advocates the synthesis, in vivo, of the chlorophyll-like Cu(II) - pheophytin. The shift of 24nm of the red absorption maximum from 681nm, corresponding to the native chlorophyll, to 657nm, corresponding to the Cu(II) - pheophytin, results in the incompatibility of P657 pigment with the photosynthetic process. Both for leaves and chloroplasts the absence of the photosensible free radicals is due to the alteration of the pigment - lipoprotein aggregates of the PSII reaction centres. Clustered species with gII = 2.26 and g = 2.08 are formed for concentration of 0.5% of Cu(II) in solution.
Chlorophyll - like Cu(II) - pheophytin prepared in vitro by ion exchange and subsequently incorporated in thin bands of cellulose, exhibits the superposition of two EPR signals : (i) one at g = 2.045 with B = 7mT, which decreases rapidly upon 02 admission, (ii) with the parameters : gII = 2.18, g = 2.04, AII = 18.8mT, A =3.3mT, aII = 1.63mT, a = 1.5mT, typical for Cu(II) - complexes with four planar N atoms in the first co-ordination sphere. The admission of H20 molecules results in a pyramidal structure with the EPR parameters similar to the pigment synthesized in vivo. The P657 pigment becomes of great value thanks to its bactericidal and bacteriostatical effects on germs both Gram - positive and Gram - negative. A new kind of medicament has to be in view, its biochemical action consisting in the alteration of the cytoplasmatic membrane of the germs. The changes of
Fig. 1 EPR spectra evolution of the local symmetry of the GU(II) cations and the
chloroplasts in different stages breaking of the coupling with the four N atoms of
of Cu(II) absorption - after 24h, the pyrole rings are responsible or the alteration of the
- after 72h, EPR spectra for P657 spectra upon-irradiation of the samples.