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Substrate inhibition in bioreactors occurs when the concentration of substrate (such as glucose, salts, or phenols [1]) 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.
Enzymes act on small molecules called substrates, which an enzyme converts into products. 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.
in which e is the concentration of free enzyme (not the total concentration) and x is the concentration of enzyme-substrate complex EA. Conservation of enzyme requires that [28] = where is now the total enzyme concentration. After combining the two expressions some straightforward algebra leads to the following expression for the concentration ...
The analysis of these reactions is much simpler if the concentration of substrate A is kept constant and substrate B varied. Under these conditions, the enzyme behaves just like a single-substrate enzyme and a plot of v by [S] gives apparent K M and V max constants for substrate B. If a set of these measurements is performed at different fixed ...
where [A] is the fixed concentration of agonist and EC 50 is the concentration of agonist that results in half maximal activation of the receptor. Whereas the IC 50 value for a compound may vary between experiments depending on experimental conditions, (e.g. substrate and enzyme concentrations) the K i is an absolute value.
They are classified according to the effect of the inhibitor on the V max (maximum reaction rate catalysed by the enzyme) and K m (the concentration of substrate resulting in half maximal enzyme activity) as the concentration of the enzyme's substrate is varied. [15] [16]
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. [1] This is unlike competitive inhibition, where binding affinity for the substrate in the enzyme is decreased in the presence of an inhibitor.
A comparison of specificity constants can also be used as a measure of the preference of an enzyme for different substrates (i.e., substrate specificity). The higher the specificity constant, the more the enzyme "prefers" that substrate. [1] The following equation, known as the Michaelis–Menten model, is used to describe the kinetics of enzymes: