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  • br Enzyme catalysis A biochemically

    2019-10-08


    Enzyme catalysis A biochemically spontaneous process proceeds in a direction where free MRS 2578 mass of the system decreases. However, every spontaneous or energetically favorable reaction needs to overcome an energy barrier known as the activation energy barrier because of the formation of an unstable transition state. Enzyme catalyzes a reaction at a faster rate by stabilizing its transition state (Fig. 1), hence lowering the activation energy, the equilibrium remains unchanged but it is achieved at a faster rate. At the total enzyme concentration, when the enzyme is saturated with the substrate, the initial velocity of the enzyme catalyzed reaction has a limiting value [4].
    Nanoparticles Nanoparticles are solid dispersion particulates of size range 10–1000 nm [10]. They cause enhancement of particle mobility, diffusion, thermal stability, storage capacity, greater surface area and also modulate the catalytic activity of attached enzymes [11], toxicity, bioavailability and solubility of various drugs [12]. Nanoparticles are very widely used in making biosensors, solar cells, photodetectors, ceramics and nanogenerators [13]. They may possess different topographies and shapes like nanotubes, nanorods, nanorings, nanowires, etc. [14]. Nanoparticles have size equivalent to that of proteins and nucleic acids present in biosystems and they have impact over them. A huge variety of modified nanostructures are being produced in association of nanoparticles with biomolecules [15]. They are broadly classified into the following types (Fig. 7).
    Enzyme-nanoparticle interaction
    Techniques to monitor enzyme nanoparticle interactions
    Structural changes in enzymes upon immobilization Conformation of enzyme always plays an important role in determining its catalytic efficiency and specificity. The process of immobilization changes the catalytic activity of enzymes through different mechanisms such as loss of its dynamic properties, alteration in conformational integrity and lesser accessibility of the active site towards substrate [91]. Immobilization process pushes the enzyme to face the environment which is different from the environment that the enzyme had in its native state. This can alter the catalytic activity of the enzyme due to diffusional limitations of the substrate or unfavorable orientation of the enzyme to perform catalysis. Immobilization of enzymes should be done to prevent deleterious conformational changes by avoiding multipoint covalent attachment procedures [92]. By analyzing the conformation of the enzyme and by evaluating the kind of forces (non-covalent) present in the enzyme, an appropriate immobilization protocol can be adopted (adsorption or covalent linkages) which can reduce the enzyme flexibility without affecting its conformation significantly. Fig. 10 shows some possible changes that an enzyme can experience during the process of immobilization. However, it is possible to determine the change in enzyme conformation due to immobilization, the prevention in changes in enzyme conformation and improvement in catalytic activity is still very complex and no such detailed protocols are available [91]. Apart from these difficulties, conformational change monitoring can be used to develop a stable enzyme preparation for a given industrial application. Following are some techniques to monitor conformational changes.
    Modulation of enzyme activity via nanoparticles Immobilization of enzymes on nanomaterials results in changes in their catalytic activity. Enzymes such as lipases are widely used in the industry for catalyzing the reactions involving the hydrolysis of carboxylic ester bonds. The substance which contains these carboxylic ester bonds are present in pharmaceutical products, food stuffs, detergents and chemical compounds used in material sciences. Immobilization of lipase on selectively reduced graphene oxide shows a significant enhancement in the catalytic activity. A surface with hydrophilic/hydrophobic interfaces is obtained by carefully controlling the reduction of graphene oxide, and binding to this surface facilitates the lid-opening dynamics without interfering with the enzyme mechanics. The lid-helix structure thus formed causes the exposure of lipase active site to the substrate in the solution [100].