Investigation of Binding‐Site Homology between Mushroom and Bacterial Tyrosinases by Using Aurones as Effectors

Tyrosinase is a copper‐containing enzyme found in plants and bacteria, as well as in humans, where it is involved in the biosynthesis of melanin‐type pigments. Tyrosinase inhibitors have attracted remarkable research interest as whitening agents in cosmetology, antibrowning agents in food chemistry, and as therapeutics. In this context, commercially available tyrosinase from mushroom (TyM) is frequently used for the identification of inhibitors. This and bacterial tyrosinase (TyB) have been the subjects of intense biochemical and structural studies, including X‐ray diffraction analysis, and this has led to the identification of structural homology and divergence among enzymes from different sources. To better understand the behavior of potential inhibitors of TyM and TyB, we selected the aurone family—previously identified as potential inhibitors of melanin biosynthesis in human melanocytes. In this study, a series of 24 aurones with different hydroxylation patterns at the A‐ and B‐rings were evaluated on TyM and TyB. The results show that, depending on the hydroxylation pattern of A‐ and B‐rings, aurones can behave as inhibitors, substrates, and activators of both enzymes. Computational analysis was performed to identify residues surrounding the aurones in the active sites of both enzymes and to rationalize the interactions. Our results highlight similarities and divergence in the behavior of TyM and TyB toward the same set of molecules.     

Dynamic aspects of cerium dioxide sintering: HT-ESEM study of grain growth and pore elimination

Sintering of CeO₂ is studied in situ by high temperature scanning environmental microscopy (HT-ESEM) at T = 1400 °C. The morphological modifications of a single grains population are recorded for 6 h. Kinetic parameters are extracted from image series. The local grain growth determined from the single population studied in situ is compared to the general grain growth obtained by classical ex situ technique. Using HT-ESEM for sintering study is validated. The grain boundary velocities range between 0 and 5 μm h⁻¹, with a mean value of about 1 μm h⁻¹. The migration of the intragranular surface pores is described. Their velocities range between 0.4 and 1.2 μm h⁻¹ and depend on pore diameters: the smaller the pore, the faster the pore velocity. The time required to fill a pore that arises at the sample surface is determined as a function of pore diameter. The time for pore elimination dependence with the pore diameters is also established.     

238Pu and 239+240Pu inventory and distribution through the lower Rhone valley terrestrial environment (Southern France)

Because of atmospheric global fallout due to thermonuclear tests performed between 1945 and 1980 and to the American SNAP 9A satellite explosion in 1964, plutonium's long-lived alpha emitter isotopes ((238)Pu, (239)Pu and (240)Pu) can be found everywhere in the environment. In the soils of the lower Rhone valley, over a surface area of approximately 11,000 km(2), existing results allow estimation of the total inventory resulting from this origin of 551 GBq as regards these radionuclides. The Marcoule Nuclear Reprocessing Plant (NRP) has been releasing (238)Pu and (239+240)Pu into the environment for over 40 years in the region and is as such a second likely source for Pu input. This article gives a global review of plutonium distribution in this particular region. It is shown that releases from Marcoule, although accounting for less than 2% of the total Pu inputs into the terrestrial environment, are responsible for localised and measurable Pu enrichments close to the facility (+2.8 GBq), and in the Rhone delta where sediments from the river settled during the past floods (+0.1 GBq). Irrigating with water from the Rhone River also allowed the transfer of approximately 3.8 GBq of (238)Pu and (239+240)Pu to the soils for the whole 1960-1998 period. These inputs, distributed over wide irrigated surface areas, do not induce significant increases of soil Pu-activity levels. In a second section, this study confirms that most of the plutonium existing in the terrestrial environment is accumulated in the soil. Less than 0.1% of the activities exist currently in the plant compartments, and the flows exported by agricultural productions are very low, although we are interested here in a French region where agriculture prevails.     

Stratification in the cohesion of biofilms grown under various environmental conditions

The objective of this study was to use indirect methods to assess the biofilm cohesion and its vertical stratification. Biofilms were grown under low hydrodynamic strengths in two reactors, a low shear stress reactor (LSSR) or under a defined shear stress in a Couette-Taylor Reactor (CTR), using different electron donors and acceptors. The stratification of biofilm cohesion was characterized from a gradual increase of the hydrodynamic strengths in terms of shear stress (erosion) and abrasion (collisions of particles). Whatever the nature of the biofilms, erosion tests demonstrated a gradual impact of a wall shear stress increase on the biofilms remaining on the substratum surface. These observations demonstrated that the biofilm cohesion was heterogeneous and increased with the biofilm depth. Both erosion and abrasion tests highlighted a basal zone of high cohesion. Investigations based on PCR-SCCP and oxygen uptake rate showed the presence of active microorganisms in this zone.     

Electroleaching and electrodeposition of zinc in a single-cell process for the treatment of solid waste

This work deals with zinc beneficiation of industrial solid waste by an electrochemical technique combining electroleaching and electrodeposition in a single-cell process. This technique is based on leaching of the solid waste by the protons generated at the anode and migration of the resulting ions toward the cathode where deposition takes place. A laboratory cell was built for testing the method. It consisted of three compartments, two electrode compartments and a solid waste chamber placed between these. Catholyte and anolyte were sulphuric/sulphate solutions at optimised concentrations. Experiments were first carried out using a zinc solution and an inert matrix in the central compartment, then using a synthetic waste prepared by dispersing zinc oxide in silicon dioxide. Best performance was obtained with treatment duration of 6h, at 4.5Adm(-2) and with catholyte circulation. In this case, a 97% of zinc oxide lixiviation and 75% of zinc-plated were achieved.     

Synthesis and characterization of a polystyrenic resin functionalized by catechol: Application to retention of metal ions

Chelating solid phase extraction is a preconcentration method adapted for metal ions extraction in water and requires functionalization of a solid sorbent by an organic ligand. A new chelating resin has been prepared by grafting catechol on Amberlite^® XAD-4 with an imine bridge and reducing it to enhance stability of the modified resin. Synthesis was first carried out at molecular level to validate experimental conditions, optimize yields and facilitate characterization of solid sorbent (particularly by FTIR). Each synthesis step of grafting on Amberlite^® XAD-4 was characterized by FTIR, Py-GC–MS and TGA-DSC. BET measurements showed a decrease in specific area after grafting from 865 to 425 m² g⁻¹ and in total pore volume from 1.19 to 0.66 cm³ g⁻¹. The grafting rate of 33% was determined by back titration of –OH (0.31 ± 0.03 mmol g⁻¹ of resin) and –NH-functions (0.93 ± 0.02 mmol g⁻¹ of resin). The increase in the sorbent hydrophilicity was confirmed by evaluating the water regain. Finally the retention properties of Cd(II), Cu(II), Ni(II) and Pb(II) were determined by ICP-AES at a pH range from 2 to 9. Retention rates of 94% and 98% were found at pH 8 for Cu(II) and Pb(II), respectively. Sorption capacities of 25.8 ± 2.5 μmol g⁻¹ for Cd(II), 89.7 ± 8.4 μmol g⁻¹ for Cu(II), 49.0 ± 10.5 μmol g⁻¹ for Ni(II) and 31.5 ± 1.6 μmol g⁻¹ for Pb(II) were measured.     

Leafamine®, a Free Amino Acid-Rich Biostimulant,Promotes Growth Performance of Deficit-Irrigated Lettuce

Water deficit causes substantial yield losses that climate change is going to make even more problematic. Sustainable agricultural practices are increasingly developed to improve plant tolerance to abiotic stresses. One innovative solution amongst others is the integration of plant biostimulants in agriculture. In this work, we investigate for the first time the effects of the biostimulant –Leafamine^®–a protein hydrolysate on greenhouse lettuce (Lactuca sativa L.) grown under well-watered and water-deficit conditions. We examined the physiological and metabolomic water deficit responses of lettuce treated with Leafamine^® (0.585 g/pot) or not. Root application of Leafamine^® increased the shoot fresh biomass of both well-watered (+40%) and deficit-irrigated (+20%) lettuce plants because the projected leaf area increased. Our results also indicate that Leafamine^® application could adjust the nitrogen metabolism by enhancing the total nitrogen content, amino acid (proline) contents and the total protein level in lettuce leaves, irrespective of the water condition. Osmolytes such as soluble sugars and polyols, also increased in Leafamine^®-treated lettuce. Our findings suggest that the protective effect of Leafamine is a widespread change in plant metabolism and could involve ABA, putrescine and raffinose.