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Enzymes are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps. The study of enzymes is called enzymology and the field of pseudoenzyme analysis recognizes that during evolution, some enzymes have lost the ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual 'pseudocatalytic' properties.
In biochemistry, allosteric regulation is the regulation of an enzyme by binding an effector molecule at a site other than the enzyme's active site.
In biochemistry, Michaelis–Menten kinetics, named after Leonor Michaelis and Maud Menten, is the simplest case of enzyme kinetics, applied to enzyme-catalysed reactions of one substrate and one product. It takes the form of an equation describing the rate reaction rate to , the concentration of the substrate A. Its formula is given by the Michaelis–Menten equation:
Maud Leonora Menten was a Canadian physician and chemist. As a bio-medical and medical researcher, she made significant contributions to enzyme kinetics and histochemistry and invented a procedure that remains in use. She is primarily known for her work with Leonor Michaelis on enzyme kinetics in 1913. The paper has been translated from its original German into English.
Chemical specificity is the ability of binding site of a macromolecule to bind specific ligands. The fewer ligands a protein can bind, the greater its specificity.
In biochemistry and molecular biology, a binding site is a region on a macromolecule such as a protein that binds to another molecule with specificity. The binding partner of the macromolecule is often referred to as a ligand. Ligands may include other proteins, enzyme substrates, second messengers, hormones, or allosteric modulators. The binding event is often, but not always, accompanied by a conformational change that alters the protein's function. Binding to protein binding sites is most often reversible, but can also be covalent reversible or irreversible.
In biochemistry, the Lineweaver–Burk plot is a graphical representation of the Michaelis–Menten equation of enzyme kinetics, described by Hans Lineweaver and Dean Burk in 1934.
In biochemistry, an Eadie–Hofstee plot is a graphical representation of the Michaelis–Menten equation in enzyme kinetics. It has been known by various different names, including Eadie plot, Hofstee plot and Augustinsson plot. Attribution to Woolf is often omitted, because although Haldane and Stern credited Woolf with the underlying equation, it was just one of the three linear transformations of the Michaelis–Menten equation that they initially introduced. However, Haldane indicated latter that Woolf had indeed found the three linear forms:
In 1932, Dr. Kurt Stern published a German translation of my book Enzymes, with numerous additions to the English text. On pp. 119–120, I described some graphical methods, stating that they were due to my friend Dr. Barnett Woolf. [...] Woolf pointed out that linear graphs are obtained when is plotted against , against , or against , the first plot being most convenient unless inhibition is being studied.
Mixed inhibition is a type of enzyme inhibition in which the inhibitor may bind to the enzyme whether or not the enzyme has already bound the substrate but has a greater affinity for one state or the other. It is called "mixed" because it can be seen as a conceptual "mixture" of competitive inhibition, in which the inhibitor can only bind the enzyme if the substrate has not already bound, and uncompetitive inhibition, in which the inhibitor can only bind the enzyme if the substrate has already bound. If the ability of the inhibitor to bind the enzyme is exactly the same whether or not the enzyme has already bound the substrate, it is known as a non-competitive inhibitor. Non-competitive inhibition is sometimes thought of as a special case of mixed inhibition.
Half maximal inhibitory concentration (IC50) is a measure of the potency of a substance in inhibiting a specific biological or biochemical function. IC50 is a quantitative measure that indicates how much of a particular inhibitory substance (e.g. drug) is needed to inhibit, in vitro, a given biological process or biological component by 50%. The biological component could be an enzyme, cell, cell receptor or microorganism. IC50 values are typically expressed as molar concentration.
In biochemistry and pharmacology, the Hill equation refers to two closely related equations that reflect the binding of ligands to macromolecules, as a function of the ligand concentration. A ligand is "a substance that forms a complex with a biomolecule to serve a biological purpose", and a macromolecule is a very large molecule, such as a protein, with a complex structure of components. Protein-ligand binding typically changes the structure of the target protein, thereby changing its function in a cell.
Non-competitive inhibition is a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate. This is unlike competitive inhibition, where binding affinity for the substrate in the enzyme is decreased in the presence of an inhibitor.
Enzyme kinetics is the study of the rates of enzyme-catalysed chemical reactions. In enzyme kinetics, the reaction rate is measured and the effects of varying the conditions of the reaction are investigated. Studying an enzyme's kinetics in this way can reveal the catalytic mechanism of this enzyme, its role in metabolism, how its activity is controlled, and how a drug or a modifier might affect the rate.
Uncompetitive inhibition is a type of inhibition in which the apparent values of the Michaelis–Menten parameters and are decreased in the same proportion.
An enzyme inhibitor is a molecule that binds to an enzyme and blocks its activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which substrate molecules are converted into products. An enzyme facilitates a specific chemical reaction by binding the substrate to its active site, a specialized area on the enzyme that accelerates the most difficult step of the reaction.
In the field of biochemistry, the specificity constant, is a measure of how efficiently an enzyme converts substrates into products. A comparison of specificity constants can also be used as a measure of the preference of an enzyme for different substrates. The higher the specificity constant, the more the enzyme "prefers" that substrate.
Victor Henri was a French-Russian physical chemist and physiologist. He was born in Marseilles as a son of Russian parents. He is known mainly as an early pioneer in enzyme kinetics. He published more than 500 papers in a variety of disciplines including biochemistry, physical chemistry, psychology, and physiology. Aleksey Krylov was his half-brother.
Competitive inhibition is interruption of a chemical pathway owing to one chemical substance inhibiting the effect of another by competing with it for binding or bonding. Any metabolic or chemical messenger system can potentially be affected by this principle, but several classes of competitive inhibition are especially important in biochemistry and medicine, including the competitive form of enzyme inhibition, the competitive form of receptor antagonism, the competitive form of antimetabolite activity, and the competitive form of poisoning.
A kinetic exclusion assay (KinExA) is a type of bioassay in which a solution containing receptor, ligand, and receptor-ligand complex is briefly exposed to additional ligand immobilized on a solid phase.
Substrate inhibition in bioreactors occurs when the concentration of substrate exceeds the optimal parameters and reduces the growth rate of the cells within the bioreactor. This is often confused with substrate limitation, which describes environments in which cell growth is limited due to of low substrate. Limited conditions can be modeled with the Monod equation; however, the Monod equation is no longer suitable in substrate inhibiting conditions. A Monod deviation, such as the Haldane (Andrew) equation, is more suitable for substrate inhibiting conditions. These cell growth models are analogous to equations that describe enzyme kinetics, although, unlike enzyme kinetics parameters, cell growth parameters are generally empirically estimated.
References
- 1 2 Wanner K, Höfner G (27 June 2007). Mass Spectrometry in Medicinal Chemistry: Applications in Drug Discovery. John Wiley & Sons. pp. 142–156. ISBN 978-3-527-61091-4.
- 1 2 3 4 Berezhkovskii AM, Szabo A, Rotbart T, Urbakh M, Kolomeisky AB (April 2017). "Dependence of the Enzymatic Velocity on the Substrate Dissociation Rate". The Journal of Physical Chemistry B. 121 (15): 3437–3442. doi:10.1021/acs.jpcb.6b09055. PMC 5577799 . PMID 28423908.
- ↑ Reuveni S, Urbakh M, Klafter J (March 2014). "Role of substrate unbinding in Michaelis-Menten enzymatic reactions". Proceedings of the National Academy of Sciences of the United States of America. 111 (12): 4391–6. Bibcode:2014PNAS..111.4391R. doi: 10.1073/pnas.1318122111 . PMC 3970482 . PMID 24616494.
- ↑ Copeland RA (2000). Enzymes a practical introduction to structure, mechanism, and data analysis. Wiley Library Catalog: J. Wiley. pp. 76–81.
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