Topic
Substrate (chemistry)
About: Substrate (chemistry) is a research topic. Over the lifetime, 35902 publications have been published within this topic receiving 740722 citations. The topic is also known as: enzyme substrate.
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TL;DR: An improved model is proposed that extends the standard endo-exo synergy model and explains the rapid decrease in hydrolysis rate and appears that the processive action of Cel7A becomes hindered by obstacles in the lignocellulose substrate.
Abstract: It is commonly observed that the rate of enzymatic hydrolysis of solid cellulose substrates declines markedly with time. In this work the mechanism behind the rate reduction was investigated using two dominant cellulases of Trichoderma reesei: exoglucanase Cel7A (formerly known as CBHI) and endoglucanase Cel7B (formerly EGI). Hydrolysis of steam-pretreated spruce (SPS) was performed with Cel7A and Cel7B alone, and in reconstituted mixtures. Throughout the 48-h hydrolysis, soluble products, hydrolysis rates, and enzyme adsorption to the substrate were measured. The hydrolysis rate for both enzymes decreases rapidly with hydrolysis time. Both enzymes adsorbed rapidly to the substrate during hydrolysis. Cel7A and Cel7B cooperate synergistically, and synergism was approximately constant during the SPS hydrolysis. Thermal instability of the enzymes and product inhibition was not the main cause of reduced hydrolysis rates. Adding fresh substrate to substrate previously hydrolyzed for 24 h with Cel7A slightly increased the hydrolysis of SPS; however, the rate increased even more by adding fresh Cel7A. This suggests that enzymes become inactivated while adsorbed to the substrate and that unproductive binding is the main cause of hydrolysis rate reduction. The strongest increase in hydrolysis rate was achieved by adding Cel7B. An improved model is proposed that extends the standard endo-exo synergy model and explains the rapid decrease in hydrolysis rate. It appears that the processive action of Cel7A becomes hindered by obstacles in the lignocellulose substrate. Obstacles created by disordered cellulose chains can be removed by the endo activity of Cel7B, which explains some of the observed synergism between Cel7A and Cel7B. The improved model is supported by adsorption studies during hydrolysis.
243 citations
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TL;DR: In vitro compartmentalization of single cells, each carrying >10(4) enzyme molecules, in a volume of <10 femtoliter (fl), enabled detection and selection despite the fast, spontaneous hydrolysis of the substrate, the very low initial thiolactonase activity of PON1, and the use of difusable fluorescent products.
242 citations
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TL;DR: In this paper, the dissolution of a metallic precursor in a supercritical fluid and the exposure of a substrate to the solution is used to reduce the precursor to its metal form by a wide variety of methods resulting in films or particles.
Abstract: Supercritical fluids (SCFs) have been used to deposit thin metal films onto a wide range of surfaces and incorporate metallic particles into different inorganic and organic substrates for microelectronic, optical and catalytic applications. The technique involves the dissolution of a metallic precursor in a SCF and the exposure of a substrate to the solution. After incorporation of the precursor with the substrate, the metallic precursor is reduced to its metal form by a wide variety of methods resulting in films or particles. The reduction methods employed are chemical reduction in the SCF with a reducing agent, such as hydrogen and alcohols, thermal reduction in the SCF and thermal decomposition in an inert atmosphere or chemical conversion with hydrogen or air. Both highly dispersed and uniformly distributed metal crystallites (
242 citations
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TL;DR: In this article, the electronic and chemical properties of a single-layer MoS2 adsorbed on Ir(111), Pd(111, or Ru(0001), three representative transition metal substrates having varying work functions but each with minimal lattice mismatch with the MoS 2 overlayer were investigated.
Abstract: Using first-principles calculations within density functional theory, we investigate the electronic and chemical properties of a single-layer MoS2 adsorbed on Ir(111), Pd(111), or Ru(0001), three representative transition metal substrates having varying work functions but each with minimal lattice mismatch with the MoS2 overlayer. We find that, for each of the metal substrates, the contact nature is of Schottky-barrier type, and the dependence of the barrier height on the work function exhibits a partial Fermi-level pinning picture. Using hydrogen adsorption as a testing example, we further demonstrate that the introduction of a metal substrate can substantially alter the chemical reactivity of the adsorbed MoS2 layer. The enhanced binding of hydrogen, by as much as ∼0.4 eV, is attributed in part to a stronger H–S coupling enabled by the transferred charge from the substrate to the MoS2 overlayer, and in part to a stronger MoS2-metal interface by the hydrogen adsorption. These findings may prove to be ins...
242 citations
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TL;DR: The aim has been to crystallographically demonstrate substrate binding and to locate the two effector-binding sites of RNR R1, and to conclude that the general allosteric effector site, located far from the active site, appears to regulate subunit interactions within the holoenzyme.
242 citations