Polyamines (PAs) are ubiquitous in cells of higher plants and play an important role in many biological functions. Because PAs affect photosynthetic oxygen evolution, this study is designed to investigate the interaction of spermine (Spm) and spermidine (Spd) cations with proteins of photosystem II (PSII) using PSII-enriched submembranes fraction with polyamine concentrations of 0.01-10 mM. Fourier transform infrared (FTIR) difference spectroscopy with its self-deconvolution and second derivative resolution enhancement as well as curve-fitting procedures was applied, in order to determine the cation binding mode, the protein conformational changes and the structural properties of cation-protein complexes. It is shown that at low polyamine concentration, cation-protein interaction (H-bonding) is through the polypeptide C=O groups with no major perturbation of the protein secondary structure. As cation concentration increases, the polyamine complexation causes significant alterations of the protein secondary structure with a decrease of the alpha-helical domains from 47% (uncomplexed PSII) up to 37% (cation complexes) and an increase in the beta-sheet structure from 18% (uncomplexed PSII) up to 29% (cation complexes). Correlations between the effects of polyamines on protein secondary structure and on the rate of oxygen evolution in PSII are also established.
Photosystem II submembrane fractions were immobilised by entrapment in poly(vinylalcohol) bearing styrylpyridinium groups (PVA-SbQ). The properties of the immobilised material, in a single-compartment micro-photoelectrochemical cell using platinum electrodes in potentiostatic mode, were compared with native (free) samples. The optimal operating conditions were investigated (electron acceptor concentration, pH, temperature, time contact and chlorophyll concentration). The photocurrent of the immobilised fractions could be inhibited by pollutants such as heavy metals (mercury, copper, lead, cadmium, chromium, nickel, and zinc) in solution. The potential for use of this system to evaluate the toxicity of sewage sludges was shown.
Abstract— The protein‐modifying agent tetranitromethane (TNM) reacts with tyrosine residues and ‐SH groups. It was found to inhibit photo synthetic electron transport on the water splitting side of photosystem II (P. V. Sane and U. Johanningmeier, Z. Naturforsch. 35c, 293–297, 1979). In the present work the inhibition by TNM is studied in detail using photosystem II submembrane fractions. It is shown that the action of TNM with membrane‐bound proteins could imply the modification of tyrosine residues. At concentrations below 30 μM and with short incubation periods (<2 min), TNM produces the release of the extrinsic polypeptides involved in the stabilization of the water‐splitting complex, this being correlated with inhibition of electron transport at a site prior to H2O2 electron donation even though the inhibition cannot be prevented by the addition of Cl or Ca2+, which are known cofactors for oxygen evolution. As the incubation period or the concentration of TNM is increased, photosynthetic pigments are bleached, starting with aggregates absorbing at relatively long wavelengths. The inhibition by low concentrations of TNM differs from the effect of most of the previously reported inhibitors acting at the oxygen‐evolving complex of photosystem II.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.