Copper effect on the protein composition of photosystem II

The definitive version is available at: http://www.blackwell-synergy.com/doi/full/10.1111/j.1399-3054.2000.1100419.xWe provide data from in vitro experiments on the polypeptide composition, photosynthetic electron transport and oxygen evolution activity of intact photosystem II (PSII) preparations under Cu(II) toxicity conditions. Low Cu(II) concentrations (Cu(II) per PSII reaction centre unit≤230) that caused around 50% inhibition of variable chlorophyll a fluorescence and oxygen evolution activity did not affect the polypeptide composition of PSII. However, the extrinsic proteins of 33, 24 and 17 kDa of the oxygen-evolving complex of PSII were removed when samples were treated with 300 μM CuCl2 (Cu(II) per PSII reaction centre unit=1 400). The LHCII antenna complex and D1 protein of the reaction centre of PSII were not affected even at these Cu(II) concentrations. The results indicated that the initial inhibition of the PSII electron transport and oxygen-evolving activity induced by the presence of toxic Cu(II) concentrations occurred before the damage of the oxygen-evolving complex. Indeed, more than 50% inhibition could be achieved in conditions where its protein composition and integrity was apparently preserved.This work was supported by the Dirección General de Investigación Científica y Técnica (Grant PB98-1632).Peer reviewe

Magnetic anisotropy and coercivity in MgO/Fe (tFe)/Ag films

Magnetic systems with reduced dimensionality show critical features, such as perpendicular surface anisotropy, enhanced magnetic moment. We have compared the magnetic properties of the iron thin films deposited by electron beam evaporation onto MgO and glass/Ag(buffer) substrates. The steps on the MgO(001) substrates of height =4.1 nm were imagined by AFM. FMR has been employed to study the magnetic anisotropy HK, and coercivity HC was measured using VSM. In the iron films on MgO substrate the strong in-plane fourfold anisotropy (K1=4.8x104 J/m3 for tFe=23nm) was observed. The anisotropy field scales with the iron film thickness. HC appeared to be significantly reduced in comparison with HK (HK=2K1/M=10xHC). This result was ascribed to the pinning effects occurring at the steps on the substrate surface. The iron films on glass/Ag were characterized by weak uniaxial anisotropy (Ku=0.28x104 J/m3) consistent with the coercivity