We carried out a detailed theoretical study on the mechanism of the carbene ligand substitution by cysteine and selenocysteine residues in an Au(I) bis-N-heterocyclic carbene complex in order to model the initial stages of the mechanism of action of this promising class of antitumor metallodrug. Both neutral and deprotonated capped Cys and Sec species were considered as possible nucleophiles in the ligand exchange reaction on the metal center to model the corresponding protein side chains. Energies and geometric structures of the possible transition states and reactant- and product-adducts involved in the substitution process have been calculated using density functional theory and local MP2. Reaction and activation enthalpies and free energies have been evaluated and indicate a slightly exothermic and exergonic process with reasonably low barriers, 21.3 and 19.6 kcal mol-1, respectively, for capped Cys and Sec, in good agreement with the experimental data available for the reaction with free amino acids. The results suggest a mechanism for the ligand exchange reaction involving an anionic thiolate or selenothiolate species coupled to an explicit proton transfer to the leaving carbene from the acidic component of the buffer. The presence of a buffer is necessary both in in vitro experiments and under physiological conditions, and its proton reservoir behavior reveals the importance of the environmental effects in carbene substitution by biological nucleophiles.Recursive elongation pathways produce compounds of increasing carbon-chain length with each iterative cycle. Of particular interest are 2-ketoacids derived from recursive elongation, which serve as precursors to a valuable class of advanced biofuels known as branched-chain higher alcohols (BCHAs). Protein engineering has been used to increase the number of iterative elongation cycles completed, yet specific production of longer-chain 2-ketoacids remains difficult to achieve. Here, we show that mitochondrial compartmentalization is an effective strategy to increase specificity of recursive pathways to favor longer-chain products. Using 2-ketoacid elongation as a proof of concept, we show that overexpression of the three elongation enzymes-LEU4, LEU1, and LEU2-in mitochondria of an isobutanol production strain results in a 2.3-fold increase in the isopentanol to isobutanol product ratio relative to overexpressing the same elongation enzymes in the cytosol, and a 31-fold increase relative to wild-type enzyme expression. Reducing the loss of intermediates allows us to further boost isopentanol production to 1.24 ± 0.06 g/L of isopentanol. In this strain, isopentanol accounts for 86% of the total BCHAs produced, while achieving the highest isopentanol titer reported for Saccharomyces cerevisiae. Localizing the elongation enzymes in mitochondria  enables the development of strains in which isopentanol constitutes as much as 93% of BCHA production. This work establishes mitochondrial compartmentalization as a new approach to favor high titers and product specificities of larger products from recursive pathways.Ditopic helicate ligands 1 and 2 were synthesized for the formation of dinuclear EuIII luminescent chiral helical assemblies (Eu2·L3) in competitive organic and protic solvent media.  https://www.selleckchem.com/products/glutathione.html  Spectroscopic analysis revealed formation of the 23 (Eu2·L3) and 22 (Eu2·L2) species in methanolic solutions. Circular dichroism and circularly polarized luminescence (CPL) spectroscopy confirmed the chiral purity of the helical systems, while scanning electron microscopy imaging demonstrated the formation of hierarchical self-assemblies with spherical morphologies.Nucleosides and purine analogues have multiple functions in cell physiology, food additives, and pharmaceuticals, and some are produced on a large scale using different microorganisms. However, biosynthesis of purines is still lacking. In the present study, we engineered the de novo purine biosynthesis pathway, branched pathways, and a global regulator to ensure highly efficient hypoxanthine production by Escherichia coli. The engineered strain Q2973 produced 1243 mg/L hypoxanthine in fed-batch fermentation, accompanied by an extremely low accumulation of byproducts such as acetate and xanthine. We also performed global gene expression analysis to illustrate the mechanism for improving hypoxanthine production. This study demonstrated the feasibility of large-scale hypoxanthine production byan engineered E. coli strain, and provides a reference for subsequent studies on purine analogues and nucleosides.Based on the mixed carboxylate ligands synthesis strategy, an indium-organic framework, (Me2NH2)1.5[In1.5(FBDC)(BDC)]·2.5NMF·CH3CN (1) has been constructed by using the mixed (2,5-di(2',5'-dicarboxylphenyl)-difluorobenzene (H4FBDC) and terephthalic acid (H2BDC). Compound 1 contains a 3D intersecting pore system which surface is modified by F atoms, and it has excellent stability in pH = 2-12 aqueous solutions. The activated 1 shows high separation for C2H2/CO2 and C2H2/CH4. Moreover, 1 not only has strong luminescence but also has the high selectivity and sensibility of fluorescence detection to nitrofurazone (NZF) in antibiotic sensing experiments, which can be used as a luminescence sensor for NZF detection.Selenoenzymes, containing a selenocysteine (Sec) residue, fulfill important roles in biology. The mammalian thioredoxin reductase selenoenzymes are key regulators of antioxidant defense and redox signaling and are inhibited by methylmercury species and by the gold-containing drug auranofin. It has been proposed that such inhibition is mediated by metal binding to Sec in the enzyme. However, direct structural observations of these classes of inhibitors binding to selenoenzymes have been few to date. Here we therefore have used extended X-ray absorption fine structure as a direct structural probe to investigate binding to the selenium site in recombinant rat thioredoxin reductase 1 (TrxR1). The results demonstrate for the first time the direct and complete binding of the metal atom of the inhibitors to the selenium atom in TrxR1 for both methylmercury and auranofin, indicating that TrxR1 inhibition indeed can be attributed to such direct metal-selenium binding.