The supplementation of monosilicic acid [Si(OH)4] to the root growing medium is known to protect plants from toxic levels of iron (Fe), copper (Cu) and manganese (Mn), but also to mitigate deficiency of Fe and Mn. However, the physicochemical bases of these alleviating mechanisms are not fully understood. Here we applied low-T electron paramagnetic resonance (EPR) spectroscopy to examine the formation of complexes of Si(OH)4 with Mn(2+), Fe(3+), and Cu(2+) in water and in xylem sap of cucumber (Cucumis sativus L.) grown without or with supply of Si(OH)4. EPR, which is also useful in establishing the redox state of these metals, was combined with measurements of total concentrations of metals in xylem sap by inductive coupled plasma. Our results show that Si(OH)4 forms coordination bonds with all three metals. The strongest interactions of Si(OH)4 appear to be with Cu(2+) (1/1 stoichiometry) which might lead to Cu precipitation. In line with this in vitro findings, Si(OH)4 supply to cucumber resulted in dramatically lower concentration of this metal in the xylem sap. Further, it was demonstrated that Si(OH)4 supplementation causes pro-reductive changes that contribute to the maintenance of Fe and, in particular, Mn in the xylem sap in bioavailable 2+ form. Our results shed more light on the intertwined reactions between Si(OH)4 and transition metals in plant fluids (e.g. xylem sap).
Papain is a protease that consists of ?-helical and ?-sheet domains which
unfold almost independently. Both, papain considerable thermal stability and
sodium dodecyl sulphate (SDS) resistance have been shown. However, the
ability of each domain to unfold upon thermal and SDS denaturation has never
been studied. This work shows that fruit papain has slightly higher thermal
inactivation resistance when it is compared to stem papain with rather high
activation energy (Ea) of 223 ? 16 kJmol-1 and Tm50 value of 79 ? 2 ?C. SDS
resistance of fruit papain was estimated by SDS-PAGE analysis and activity
staining. It has been noted that, in the presence of SDS, unless heat energy
was applied in order to unfold papain, the protein remained active.
Furthermore, it has been proven via Fourier transform infrared spectroscopy
(FT-IR) that ?-helical domain of fruit papain is more prone to unfolding at
elevated temperatures and in the presence of SDS then ?-sheet rich domain.
Thermal denaturation of papain without detergent present led to accelerated
formation of aggregation specific intermolecular ?-sheets as compared to
native protein. Presented results are both, of fundamental and application
importance.
Coordinate and redox interactions of epinephrine (Epi) with iron at physiological pH are essential for understanding two very different phenomena – the detrimental effects of chronic stress on the cardiovascular system and the cross-linking of catecholamine-rich biopolymers and frameworks. Here we show that Epi and Fe3+ form stable high-spin complexes in the 1:1 or 3:1 stoichiometry, depending on the Epi/Fe3+ concentration ratio (low or high). Oxygen atoms on the catechol ring represent the sites of coordinate bond formation within physiologically relevant bidentate 1:1 complex. Redox properties of Epi are slightly impacted by Fe3+. On the other hand, Epi and Fe2+ form a complex that acts as a strong reducing agent, which leads to the production of hydrogen peroxide via O2 reduction, and to a facilitated formation of the Epi–Fe3+ complexes. Epi is not oxidized in this process, i.e. Fe2+ is not an electron shuttle, but the electron donor. Epi-catalyzed oxidation of Fe2+ represents a plausible chemical basis of stress-related damage to heart cells. In addition, our results support the previous findings on the interactions of catecholamine moieties in polymers with iron and provide a novel strategy for improving the efficiency of cross-linking.
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