SummaryPhotosynthetic organisms such as plants, algae and some cyanobacteria synthesize tocochromanols, a group of compounds that encompasses tocopherols and tocotrienols and that exhibits vitamin E activity in animals. While most vitamin E biosynthetic genes have been identified in plant genomes, regulatory genes controlling tocopherol accumulation are currently unknown.We isolated by forward genetics Arabidopsis enhanced vitamin E (eve) mutants that overaccumulate the classic tocopherols and plastochromanol-8, and a tocochromanol unknown in this species. We mapped eve1 and eve4, and identified the unknown Arabidopsis tocochromanol by using a combination of analytical tools. In addition, we determined its biosynthetic pathway with a series of tocochromanol biosynthetic mutants and transgenic lines.eve1 and eve4 are two seed lipid mutants affecting the WRINKLED1 (WRI1) and ACYL-COA:DIACYLGLYCEROL ACYLTRANSFERASE1 (DGAT1) genes, respectively. The unknown tocochromanol is 11 0 -12 0 c-tocomonoenol, whose biosynthesis is VITAMIN E 1 (VTE1) -and VTE2-dependent and is initiated by the condensation of homogentisate (HGA) and tetrahydrogeranylgeranyl pyrophosphate. This study identifies the first two regulatory genes, WRI1 and DGAT1, that control the synthesis of all tocochromanol forms in seeds, and shows the existence of a metabolic trade-off between lipid and tocochromanol metabolisms. Moreover, it shows that Arabidopsis possesses a tocomonoenol biosynthetic pathway that competes with tocopherol synthesis.
Anaerobic microorganisms of the Geobacter genus are effective electron sources for the synthesis of nanoparticles, for bioremediation of polluted water, and for the production of electricity in fuel cells. In multistep reactions, electrons are transferred via iron/heme cofactors of c‐type cytochromes from the inner cell membrane to extracellular metal ions, which are bound to outer membrane cytochromes. We measured electron production and electron flux rates to 5×105 e s−1 per G. sulfurreducens. Remarkably, these rates are independent of the oxidants, and follow zero order kinetics. It turned out that the microorganisms regulate electron flux rates by increasing their Fe2+/Fe3+ ratios in the multiheme cytochromes whenever the activity of the extracellular metal oxidants is diminished. By this mechanism the respiration remains constant even when oxidizing conditions are changing. This homeostasis is a vital condition for living systems, and makes G. sulfurreducens a versatile electron source.
Carbon monoxide releasing molecules (CORMs) are investigated widely in synthetic and medicinal chemistry owing to the potential therapeutic applications of the CO gas. Organometallic carbonyl complexes are best suited to play the role of CO carriers as they allow the exogenous release of CO under controlled conditions, and the toxicity of the gas can be overcome. With the long‐term goal of developing CORMs with similar properties to those of the sesta‐methoxyisobutylisonitrile (sesta‐mibi) 99mTc complex (Cardiolite), we have studied the reactivity of isocyanide ligands towards 16‐ and 17‐electron cis‐[Re(CO)2Br4]–/2– species and the [Mn(CO)5Br] complex. Six different isocyanide ancillary ligands (CNR), including mibi, were selected for this study. Their reactions with cis‐dicarbonyl ReIII and ReII complexes were accompanied by two‐ and one‐electron reduction of the metal center and resulted in the formation of stable cis‐mer‐[Re(CO)2(CNR)3Br] species, whereas the same reactions with [Mn(CO)5Br] gave fac‐[Mn(CO)3(CNR)2Br] compounds. All of the complexes were fully characterized, and single‐crystal X‐ray diffraction structure determinations were performed for selected species. In addition, unique monocarbonyl complexes were obtained from the reactions of cis‐[Re(CO)2Br4]– (1) with tert‐butyl isocyanide and cis‐[Re(CO)2Br4]2– (2) with mibi. The species, a heptacoordinate ReIII and a hexacoordinate ReII complex, respectively, were also characterized structurally. The CO‐releasing profiles, the cytotoxic effects against 3T3 fibroblast cells, and the antibacterial properties of the compounds were also investigated.
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