Search results for "substrate"
showing 10 items of 1018 documents
Are biological classifications of headwater streams concordant across multiple taxonomic groups?
2003
Summary 1. Studies assessing human impacts on freshwater ecosystems are typically based on a single taxonomic group, often macroinvertebrates or fish. Unfortunately, the degree to which such macroinvertebrate or fish-based surveys can be generalised across other taxonomic groups remains largely unknown. A prerequisite for useful generalisations is that different taxonomic groups exhibit concordant patterns of community structure across sites. 2. We examined the concordance among fish, benthic macroinvertebrates and bryophytes in 32 streams in a boreal catchment in Finland. Our goal was to test how consistently different taxonomic groups classify stream sites; for example, can site groupings…
Lysine synthesis control in Corynebacterium glutamicum RC 115 in mixed substrate (glucose-acetate) medium.
2003
The effect of acetate as a glucose co-substrate on growth, lysine synthesis and experimental lysine yield from carbon substrates by Corynebacterium glutamicum RC 115 was investigated. It was found that low amounts of acetate, injected with a glucose-acetate pulse into the steady-state continuous culture in bioreactor, caused a slight decrease in the specific rates of glucose uptake and bacterial growth, but a significant increase in the cell specific rate of lysine synthesis and an increase in lysine yield. In contrast, acetate injected in high amounts was followed by a drastic decrease in the values of these parameters. A strong increase in experimental lysine yield under the latter condit…
Chemo-enzymatic Conversion of Glucose in 5-Hydroxymethylfurfural: The Joint Effect of Ionic Liquids and Ultrasound
2020
For the valorization of lignocellulosic biomass, a key step is unlocking the conversion of glucose to suitable chemical platforms. To this aim, we herein describe the sequential chemo-enzymatic conversion of glucose into 5-hydroxymethylfurfural (5-HMF), in two steps: glucose isomerization to fructose, catalyzed by glucose isomerase (GI) and fructose dehydration to 5-HMF promoted by Amberlyst 15. The novelty of our approach lies in the use of crude cell extracts of Streptomyces coelicolor showing GI activity, as isomerization catalysts, along with a commercial immobilized GI. Under optimized reaction conditions, we obtained a conversion to 5-HMF (C5‑HMF) from glucose of 50% in the H2O/[bmim]…
Active Site Mapping of Xylan-Deconstructing Enzymes with Arabinoxylan Oligosaccharides Produced by Automated Glycan Assembly
2017
Xylan-degrading enzymes are crucial for the deconstruction of hemicellulosic biomass, making the hydrolysis products available for various industrial applications such as the production of biofuel. To determine the substrate specificities of these enzymes, we prepared a collection of complex xylan oligosaccharides by automated glycan assembly. Seven differentially protected building blocks provided the basis for the modular assembly of 2-substituted, 3-substituted, and 2-/3-substituted arabino- and glucuronoxylan oligosaccharides. Elongation of the xylan backbone relied on iterative additions of C4-fluorenylmethoxylcarbonyl (Fmoc) protected xylose building blocks to a linker-functionalized …
Effect of mode of operation, substrate and final electron acceptor on single-chamber membraneless microbial fuel cell operating with a mixed community
2018
Abstract Waste minimization and circular thinking are to be achieved in order to cope with the limited amount of resources of our planet. In this perspective, bio-electrochemical systems (BESs) can contribute to the global balance with their ability to extract chemical residual energy from wastewater and transform it directly into electrical current. BESs development has been limited by the cost connected to reactor design, in which membranes and cathode catalyst constituted a major drawback. In this paper we report the optimization process of a simple reactor without membranes or precious catalyst that produced 47.1 mW m−2, which is more than what achieved with configurations including mem…
Model-based biotechnological potential analysis of Kluyveromyces marxianus central metabolism
2016
Abstract The non-conventional yeast Kluyveromyces marxianus is an emerging industrial producer for many biotechnological processes. Here, we show the application of a biomass-linked stoichiometric model of central metabolism that is experimentally validated, and mass and charge balanced for assessing the carbon conversion efficiency of wild type and modified K. marxianus. Pairs of substrates (lactose, glucose, inulin, xylose) and products (ethanol, acetate, lactate, glycerol, ethyl acetate, succinate, glutamate, phenylethanol and phenylalanine) are examined by various modelling and optimisation methods. Our model reveals the organism’s potential for industrial application and metabolic engi…
Probing suggested catalytic domains of glycosyltransferases by site-directed mutagenesis.
2003
The plant enzyme arbutin synthase isolated from cell suspension cultures of Rauvolfia serpentina and heterologously expressed in Escherichia coli is a member of the NRD1beta family of glycosyltransferases. This enzyme was used to prove, by site-directed mutagenesis, suggested catalytic domains and reaction mechanisms proposed for enzyme-catalyzed glycosylation. Replacement of amino acids far from the NRD domain do not significantly affect arbutin synthase activity. Exchange of amino acids at the NRD site leads to a decrease of enzymatic activity, e.g. substitution of Glu368 by Asp. Glu368, which is a conserved amino acid in glycosyltransferases located at position 2 and is important for enz…
Synthesis of phosphono dipeptides, inhibitors of cathepsin C
1998
Abstract Phosphono dipeptides containing glycine, glycylglycine or L-alanine at N-termini and racemic phosphonic acid analogues of aromatic amino acids, as well as racemic alicyclic aminophosphonates, exhibit moderate inhibitory activity towards cathepsin C. This activity is probably due to the binding of the phosphonate moiety by a positively charged part of the enzyme which is complementary to the carboxylate part of the synthetic dipeptide products of the enzymatic reaction.
Influence of metal–support interaction on the surface structure of gold nanoclusters deposited on native SiOx/Si substrates
2014
The structure of small gold nanoclusters (R ~ 2.5 nm) deposited on different silica on silicon substrates is investigated using several characterization techniques (AFM, XRD, EXAFS and GISAXS). The grain morphology and the surface roughness of the deposited gold clusters are determined by AFM. The in-plane GISAXS intensity is modelled in order to obtain information about the cluster size and the characteristic length scale of the surface roughness. AFM and GISAXS results are in excellent agreement and show that the surface morphology of the deposited clusters depends on whether defect-rich (native) or defect-free (thermal) silica is used as a substrate. Gold clusters show a strong tendency …
Oxidative DNA base damage induced by singlet oxygen and photosensitization: recognition by repair endonucleases and mutagenicity.
2000
We have analyzed the recognition by various repair endonucleases of DNA base modifications induced by three oxidants, viz. [4-(tert-butyldioxycarbonyl)benzyl]triethylammonium chloride (BCBT), a photochemical source of tert-butoxyl radicals, disodium salt of 1,4-etheno-2,3-benzodioxin-1,4-dipropanoic acid (NDPO(2)), a chemical source of singlet oxygen, and riboflavin, a type-I photosensitizer. The base modifications induced by BCBT, which were previously shown to be mostly 7,8-dihydro-8-oxoguanine (8-oxoGua) residues, were recognized by Fpg and Ogg1 proteins, but not by endonuclease IIII, Ntg1 and Ntg2 proteins. In the case of singlet oxygen induced damage, 8-oxoGua accounted for only 35% of…