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Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. The study of how fast an enzyme can transform a substrate into a product is called enzyme kinetics. The rate of reaction of many chemical reactions shows a linear response as function of the concentration of substrate molecules.
The rate of the enzyme-catalysed reaction is limited by diffusion and so the enzyme 'processes' the substrate well before it encounters another molecule. [1] Some enzymes operate with kinetics which are faster than diffusion rates, which would seem to be impossible. Several mechanisms have been invoked to explain this phenomenon.
The reaction catalysed by an enzyme uses exactly the same reactants and produces exactly the same products as the uncatalysed reaction. Like other catalysts, enzymes do not alter the position of equilibrium between substrates and products. [1] However, unlike uncatalysed chemical reactions, enzyme-catalysed reactions display saturation kinetics.
A decade before Michaelis and Menten, Victor Henri found that enzyme reactions could be explained by assuming a binding interaction between the enzyme and the substrate. [11] His work was taken up by Michaelis and Menten, who investigated the kinetics of invertase, an enzyme that catalyzes the hydrolysis of sucrose into glucose and fructose. [12]
Saturation happens because, as substrate concentration increases, more and more of the free enzyme is converted into the substrate-bound ES complex. At the maximum reaction rate (V max) of the enzyme, all the enzyme active sites are bound to substrate, and the amount of ES complex is the same as the total amount of enzyme. [1]: 8.4
Similar reactions will occur far faster if the reaction is intramolecular. The effective concentration of acetate in the intramolecular reaction can be estimated as k 2 /k 1 = 2 x 10 5 Molar. However, the situation might be more complex, since modern computational studies have established that traditional examples of proximity effects cannot be ...
Both enzymes that have been more or less isolated and enzymes still residing inside living cells are employed for this task. [1] [2] [3] Modern biotechnology, specifically directed evolution, has made the production of modified or non-natural enzymes possible. This has enabled the development of enzymes that can catalyze novel small molecule ...
By lowering the activation energy, the enzyme speeds up that reaction by a rate of 10 11 or more; a reaction that would normally take over 3,000 years to complete spontaneously might take less than a second with an enzyme. The enzyme itself is not used up in the process and is free to catalyze the same reaction with a new set of substrates.