INTRODUCTION
David M. Gibson, Robert A. Harris in Metabolic Regulation in Mammals, 2001
bach enzyme catalyst possesses a region designated the "active site" where the specific rcactants (substrates) bind tightly but revcrsibly. Depending on the concentrations of the substrates and the enzyme in solution the amount of the enzyme-substrate complcx formed in this very rapid equilibration will usually determine the rate at which the reaction will proceed. The active sites are physical templates constructed with certain of the projecting amino acid side chains of the enzyme (figure 1.4). Variously chargée! or hydrophobic in nature, the three-dimensional arrangements of side chains not only restrict what particular substrates can bind but also define the precise orientations of the bound substrates to each other. Indeed the catalytic efficiency of an enzyme depends on the exquisite alignment of the interacting domains of the substrates. The coupling of one enzyme system with another through a common intermediate also depends on stereospecilic binding of substrates (and products) to cognate enzymes. litis is facilitated if sequential enzymes are placed near each other, or bound to each other. The extreme is DNA/RNA template-ordered synthetic steps (Figures 1.5 and 1.6).
Future Strategies for Commercial Biocatalysis
Peter Grunwald in Pharmaceutical Biocatalysis, 2019
In order to assemble one-pot cascades such as the example in Fig. 1.2, as with any biocatalytic reaction, it is necessary to choose the most appropriate enzymes to start with based on clear selection criteria as well as compatibility with other enzymes in the cascade. Selection criteria are often focused on enzyme kinetics and catalytic efficiency. Other key criteria are enzyme stability and optima of activity under the reaction conditions (e.g., temperature, pH, and salt concentrations), substrate or product inhibition (including products downstream in the cascade), cofactor requirements and options for cofactor recycling either by additional enzymes or by enzymes within the cascade. An example of this cofactor recycling within a cellular pathway or cascade system is the cycling of NAD+ and NADH in the production of ethanol by Saccharomyces cerevisiae through the Embden–Meyerhof pathway. In this system the transformation of glyceraldehyde-3-phosphate to 1,3-diphosphoglycerate converts NAD+ to NADH whereas the final step to ethanol from acetaldehyde catalysed by alcohol dehydrogenase converts NADH to NAD+, meaning that the system is self-sufficient for this cofactor. In the sugar synthesis example described above, ATP and NAD+ recycling was achieved through two additional enzymes that were not part of the pathway or cascade but were present solely for recycling. A further key criterion is the commercial availability of an enzyme or the ability to readily produce the enzyme in an active and soluble form in a recombinant microbial production system.
Relevance of Catalytic Anti-VIP Antibodies to the Airway
Sami I. Said in Proinflammatory and Antiinflammatory Peptides, 2020
There are two reasons to expect proteolytic antibodies to be biologically more potent than reversibly binding antibodies. First, cleavage of the target polypeptide can be anticipated to produce fragments with biological activity distinct from the parent polypeptide. Second, a single catalyst molecules can cleave multiple substrate molecules, whereas noncatalytic antibodies can act only stoichiometrically. The catalytic efficiency of proteolytic autoantibodies and recombinant antibody fragments is sufficiently great to suggest that they are functionally important. The case of VIP is discussed here. This polypeptide elicits its biological effects in the airways and other tissues at picomolar to nanomolar concentrations, which are lower than the Km values observed for antibodies (nanomolar range) and proteolytic enzymes (micromolarmillimolar range). At VIP concentrations lower than the Km of the catalyst, the rate of proteolysis is given by the ratio kcatJKm (catalytic efficiency), where l/Km approximates the VIP-binding affinity, and kCat denotes turnover number. Recombinant antibody fragments with catalytic efficiency comparable to highly evolved conventional proteases have been isolated (20), and autoantibodies found in blood display even greater catalytic efficiency. Antibodies are found in physiological fluids at far greater concentrations than conventional enzymes. The IgG concentration in serum is about 70 μM. In multiple myeloma patients, the antibody and antibody light-chain products of the tumor cells accumulate in serum and urine to millimolar levels (40). At these concentrations, it appears most unlikely that the proteolytic activity is biologically inconsequential.
Nanoparticles in nanomedicine: a comprehensive updated review on current status, challenges and emerging opportunities
Published in Journal of Microencapsulation, 2021
Heidi Mohamed Abdel-Mageed, Nermeen Zakaria AbuelEzz, Rasha Ali Radwan, Saleh Ahmed Mohamed
Intriguingly, nanoparticles with ‘enzyme-mimetic’ activity have been studied as alternatives to natural enzymes. Catalytically active nanomaterials specifically in Nanohybrid iron oxide NP formulation and preparation allowed the introduction of enzyme mimetics, possessing peroxidase, oxidase, superoxide dismutase and catalase-like activities (nanozymes) (Singh 2019). The field of nanozymes offers promising new biomedical applications, from biofilm disruption to neurodegeneration protection and cancer prevention however, it is still in its infancy (Cormode et al.2018). Studies published are remarkable nonetheless several questions still are unanswered, which endorses further research pursue. The interwoven relationship between catalytic efficiency, therapeutic activity and biocomptability is yet to be resolved. High-performance nanozymes and highly selective nanozymes are to be developed to match catalytic efficiency natural enzymes. Also problems with batch-to-batch variation in size and shape of nanoparticles/nanozymes, and thus variations in physicochemical characteristics, demands more emphasis on optimising the synthesis protocol for production of monodispersed nanozymes. In view of the discussed points it is evident that nanomedicine research arena is yet to fully mature to revolutionise the field of human medicine. High demand of investments, scientific and technical limits and overfilling sellers and marketing challenges such as excessive therapeutics prices and limited market penetration are obstacles that demand attention to enhance the potential of nanoparticle drug delivery share.
Electrochemical immunoassay for tumor markers based on hydrogels
Published in Expert Review of Molecular Diagnostics, 2018
In electrochemical immunoassays, catalytic reactions can significantly amplify signal responses and sensitivity [27,52]. A number of nanocatalysts (nanoparticle-based catalysts) [53–56] have aroused increasing attention, owning to their high catalytic activity, good conductivity, and robustness in harsh conditions. Notably, hybrid nanocatalysts with multicomponent nanostructures possess improved catalytic activity due to the synergistic effect of the contained components [55,57]. For instance, bimetallic Au/Pt exhibits higher catalytic ability for H2O2 than monometallic Pt or Au [27]. In addition, PdNP-loaded carbon nanofibers have shown excellent electrocatalytic activity toward the redox of H2O2 and nicotinamide adenine dinucleotide (NADH) [58]. Moreover, the catalytic efficiency is significantly affected by the amount and activity of catalysts, and outstanding electronic transmission capacity of the sensing interface [43].
Advances in detection of hazardous organophosphorus compounds using organophosphorus hydrolase based biosensors
Published in Critical Reviews in Toxicology, 2019
Monika Jain, Priyanka Yadav, Abhijeet Joshi, Prashant Kodgire
OPH has quite a broad substrate specificity implying a plastic active site (Reeves et al. 2008; Wales and Reeves 2012). The broad substrate specificity is due to the nonspecific substrate binding site (Bigley and Raushel 2013). The rate-limiting step and the catalytic efficiency are dependent on the pKa of the leaving group (Ghanem and Raushel 2005). The enzyme is found to have the highest efficiency for hydrolyzing the electron withdrawing phenolic leaving groups, but it also cleaves the halide bond and thiol linkage (Bigley and Raushel 2013). The surface of the enzyme has three hydrophobic pockets, to which the three esters groups of substrates interact. The leaving group pocket is made up of the residues W131, F132, F306, and Y309. These residues largely govern the specificity of the leaving group. The other ester groups interact with the large and small pocket. This determines the specificity of the side ester groups of the substrate. In the hydrolysis reaction of organophosphate, the enzyme exhibits a significant amount of stereoselectivity. In the hydrolysis reaction of the racemic mixture, the enzyme prefers the Sp enantiomer over the Rp enantiomer. When the actual bond cleavage is the rate-limiting step, the corresponding phosphate esters are found to be hydrolyzed slower than the thiophosphate esters. And when the rate limiting step is associated with the conformational step or product release then the hydrolysis of phosphate esters is found to be faster than the thiophosphate esters (Raushel and Holden 2000; Bigley and Raushel 2013).
Related Knowledge Centers
- Biochemistry
- Enzyme
- Enzyme Kinetics
- Turnover Number
- Substrate
- Product
- Reaction Rate Constant
- Diffusion-Limited Enzyme