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Conjugated methyl sulfide and phenyl sulfide derivatives of oxidosqualene as inhibitors of oxidosqualene and squalene-hopene cyclases.

Various (1E,3E)- and (1Z,3E)-conjugated methylthio derivatives of oxidosqualene (OS) and conjugated and non-conjugated phenylthio derivatives of OS were obtained. These compounds, designed as inhibitors of pig liver and Saccharomyces cerevisiae 2,3-oxidosqualene-lanosterol cyclases (OSC) (EC 5.4.99.7) and of Alicyclobacillus acidocaldarius squalene-hopene cyclase (SHC) (EC 5.4.99.-), contain the reactive function adjacent to carbons involved in the formation of the third and the fourth cycle during OS cyclization. All the new compounds are inhibitors of OSC and SHC, with various degrees of selectivity. The conjugated methylthio derivatives behaved as potent inhibitors of S. cerevisiae OSC, whereas most of the phenylthio derivatives were especially active toward SHC.

Animals↗

Enzyme-mediated sulfide production for the reconstitution of [2Fe-2S] clusters into apo-biotin synthase of Escherichia coli. Sulfide transfer from cysteine to biotin.

We previously showed that biotin synthase in which the (Fe-S) cluster was labelled with 34S by reconstitution donates 34S to biotin [B. Tse Sum Bui, D. Florentin, F. Fournier, O. Ploux, A. Méjean & A. Marquet (1998) FEBS Lett. 440, 226-230]. We therefore proposed that the source of sulfur was very likely the (Fe-S) centre. This depletion of sulfur from the cluster during enzymatic reaction could explain the absence of turnover of the enzyme which means that to restore a catalytic activity, the clusters have to be regenerated. In this report, we show that the NifS protein from Azotobacter vinelandii and C-DES from Synechocystis as well as rhodanese from bovine liver can mobilize the sulfur, respectively, from cysteine and thiosulfate for the formation of a [2Fe-2S] cluster in the apoprotein of Escherichia coli biotin synthase. The reconstituted enzymes were as active as the native enzyme. When [35S]cysteine was used during the reconstitution experiments in the presence of NifS, labelled (Fe35S) biotin synthase was obtained. This enzyme produced [35S]biotin, confirming the results obtained with the 34S-reconstituted enzyme. NifS was also effective in mobilizing selenium from selenocystine to produce an (Fe-Se) cluster. However, though NifS could efficiently reconstitute holobiotin synthase from the apoform, starting from cysteine, these two effectors had no significant effect on the turnover of the enzyme in the in vitro assay.

Bacterial Proteins↗

Leaching of zinc sulfide by Thiobacillus ferrooxidans: bacterial oxidation of the sulfur product layer increases the rate of zinc sulfide dissolution at high concentrations of ferrous ions.

This paper reports the results of leaching experiments conducted with and without Thiobacillus ferrooxidans at the same conditions in solution. The extent of leaching of ZnS with bacteria is significantly higher than that without bacteria at high concentrations of ferrous ions. A porous layer of elemental sulfur is present on the surfaces of the chemically leached particles, while no sulfur is present on the surfaces of the bacterially leached particles. The analysis of the data using the shrinking-core model shows that the chemical leaching of ZnS is limited by the diffusion of ferrous ions through the sulfur product layer at high concentrations of ferrous ions. The analysis of the data shows that diffusion through the product layer does not limit the rate of dissolution when bacteria are present. This suggests that the action of T. ferrooxidans in oxidizing the sulfur formed on the particle surface is to remove the barrier to diffusion by ferrous ions.

Electrolysis↗

Cadmium sulfide and cadmium selenide/cadmium sulfide nanoparticles stabilized in water with poly(cysteine acrylamide).

Cysteine acrylamide (N-acryloyl L-cysteine) stabilizes CdS nanoparticles as the particles form in aqueous dispersions. Cysteine acrylamide also exchanges for citrate on the surfaces of CdSe and core/shell CdSe/CdS nanoparticles to provide greater stability. Heating of the nanoparticle dispersions polymerizes the cysteine acrylamide on the surface to form a more efficient polydentate stabilizer. The polymer-coated nanoparticle dispersions are colloidally stable even after removal of low molecular weight solutes by dialysis. Emission quantum yields of the polymer-coated CdSe and CdSe/CdS samples were 0.9% and 2.6%, respectively, after aging of the samples in light. CdSe/CdS coated with poly(cysteine acrylamide) is colloidally stable for at least two years in the dark at 5 degrees C.

Acrylic Resins↗