Enzymes are biocatalysts that speed up the reactions taking place inside the cell. They are widely used in industries, scientific research and clinical diagnostics. Enzymes are specific for their ...substrates. They increase the rate of reaction by lowering the activation energy required to convert the substrates into the products. The catalysis by an enzyme is influenced by the nature of medium, substrate, enzyme concentration, temperature, pH, and the presence of activators and inhibitors. Nanoparticles are solid dispersion particulates of size range 10–1000 nm. They cause enhancement of particle mobility, diffusion, thermal stability, storage capacity, greater surface area and also modulate catalytic activity of the attached enzymes. Enzymes can be immobilized on nanoparticles by simple adsorption or via chemical linkages. Immobilization is a commercially applicable and a convenient method because it usually results in enhanced thermal and pH stabilities of the enzyme, lower cost of production, reusability with easy handling and separation. Primary objective of writing this review is to give an overview of the various aspects of enzymology, enzyme catalysis, enzyme immobilization and modulation of enzyme activity with special emphasis on modulation through different types of nanoparticles including their synthesis, characterization and applications.
•Enzymes are biocatalysts and have wide applications.•Enzyme catalysis is influenced by a number of factors.•A variety of nanostructures are being synthesized.•Enzymes can be immobilized on nanoparticles by adsorption or via chemical linkages.•Nanoparticles modulate activity and usually increase the stability of bound enzymes.
•Radical SAM enzymes use SAM and a 4Fe–4S cluster for diverse catalytic reactions.•GREs catalyze reactions through production of glycyl, thiyl, and substrate radicals.•PFL-AE has provided insights ...into active site of radical SAM enzymes.•PFL-AE established how activating enzymes interact with their substrate GREs.
The glycyl radical enzyme activating enzymes (GRE–AEs) are a group of enzymes that belong to the radical S-adenosylmethionine (SAM) superfamily and utilize a 4Fe–4S cluster and SAM to catalyze H-atom abstraction from their substrate proteins. GRE–AEs activate homodimeric proteins known as glycyl radical enzymes (GREs) through the production of a glycyl radical. After activation, these GREs catalyze diverse reactions through the production of their own substrate radicals. The GRE–AE pyruvate formate lyase activating enzyme (PFL-AE) is extensively characterized and has provided insights into the active site structure of radical SAM enzymes including GRE–AEs, illustrating the nature of the interactions with their corresponding substrate GREs and external electron donors. This review will highlight research on PFL-AE and will also discuss a few GREs and their respective activating enzymes.
Poulos analyzes heme enzyme structure and function, focusing on peroxidases, cytochrome P450, nitric oxide synthase, chloroperoxidase, and heme oxygenase. While oxygenases rely on oxygen to oxidize, ...peroxidases utilize hydrogen peroxide for this function.
Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ...ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.
PcMulGH9, a novel glycoside hydrolase family 9 (GH9) from
Paenibacillus curdlanolyticus
B-6, was successfully expressed in
Escherichia coli
. It is composed of a catalytic domain of GH9, two domains ...of carbohydrate-binding module family 3 (CBM3) and two domains of fibronectin type 3 (Fn3). The PcMulGH9 enzyme showed broad activity towards the β-1,4 glycosidic linkages of cellulose, mannan and xylan, including cellulose and xylan contained in lignocellulosic biomass, which is rarely found in GH9. The enzyme hydrolysed substrates with bifunctional endo-/exotypes cellulase, mannanase and xylanase activities, but predominantly exhibited exo-activities. This enzyme released cellobiose as a major product from cellohexaose, while mannotriose and xylotriose were major hydrolysis products from mannohexaose and xylohexaose, respectively. Moreover, PcMulGH9 could hydrolyse untreated corn hull and rice straw into xylo- and cello-oligosaccharides. Enzyme kinetics, site-directed mutagenesis and molecular docking revealed that Met394, located at the binding subsite + 2, was involved in broad substrate specificity of PcMulGH9 enzyme. This study offers new knowledge of the multifunctional cellulase/mannanase/xylanase in GH9. The PcMulGH9 enzyme showed a novel function of GH9, which increases its potential for saccharification of lignocellulosic biomass into value-added products, especially oligosaccharides.
The authors report on a chromogenic system based MnO.sub.2 nanosheet and the chomgenic substrate 3,3',5,5'-tetramethylbenzidine (TMB). The MnO.sub.2 nanosheet can oxidize TMB in acidic environment to ...form a yellow solution with an absorption peak at 450 nm. The process does not require the presence of an enzyme or H.sub.2O.sub.2. However, on addition of ferrous ion to the chromogenic system, the MnO.sub.2 nanosheet is decomposed via the redox reaction that occurs between Fe(II) and MnO.sub.2. As a result, the intensity of the absorption at 450 nm is reduced. This finding is exploited in a photometric method for determination of Fe(II) that shows high selectivity and a 0.3 muM detection limit (based on the 3sigma/slope criterion). Fe(II) can also be detected visually in concentrations down to 100 muM. The method was applied to the determination of Fe(II) in spiked water samples and gave satisfactory recoveries.
Immobilization of enzymes may produce alterations in their observed activity, specificity or selectivity. Although in many cases an impoverishment of the enzyme properties is observed upon ...immobilization (caused by the distortion of the enzyme due to the interaction with the support) in some instances such properties may be enhanced by this immobilization. These alterations in enzyme properties are sometimes associated with changes in the enzyme structure. Occasionally, these variations will be positive. For example, they may be related to the stabilization of a hyperactivated form of the enzyme, like in the case of lipases immobilized on hydrophobic supports via interfacial activation. In some other instances, these improvements will be just a consequence of random modifications in the enzyme properties that in some reactions will be positive while in others may be negative. For this reason, the preparation of a library of biocatalysts as broad as possible may be a key turning point to find an immobilized biocatalyst with improved properties when compared to the free enzyme. Immobilized enzymes will be dispersed on the support surface and aggregation will no longer be possible, while the free enzyme may suffer aggregation, which greatly decreases enzyme activity. Moreover, enzyme rigidification may lead to preservation of the enzyme properties under drastic conditions in which the enzyme tends to become distorted thus decreasing its activity. Furthermore, immobilization of enzymes on a support, mainly on a porous support, may in many cases also have a positive impact on the observed enzyme behavior, not really related to structural changes. For example, the promotion of diffusional problems (e.g., pH gradients, substrate or product gradients), partition (towards or away from the enzyme environment, for substrate or products), or the blocking of some areas (e.g., reducing inhibitions) may greatly improve enzyme performance. Thus, in this tutorial review, we will try to list and explain some of the main reasons that may produce an improvement in enzyme activity, specificity or selectivity, either real or apparent, due to immobilization.
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