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Michaelis-Menten : ウィキペディア英語版
Michaelis–Menten kinetics

In biochemistry, Michaelis–Menten kinetics is one of the best-known models of enzyme kinetics. It is named after German biochemist Leonor Michaelis and Canadian physician Maud Menten. The model takes the form of an equation describing the rate of enzymatic reactions, by relating reaction rate v to (), the concentration of a substrate ''S''. Its formula is given by
: v = \frac = \frac + ()} .
Here, V_\max represents the maximum rate achieved by the system, at maximum (saturating) substrate concentrations. The Michaelis constant K_\mathrm is the substrate concentration at which the reaction rate is half of V_\max.〔http://www.worthington-biochem.com/introbiochem/substrateconc.html〕 Biochemical reactions involving a single substrate are often assumed to follow Michaelis–Menten kinetics, without regard to the model's underlying assumptions.
==Model==

In 1903, French physical chemist Victor Henri found that enzyme reactions were initiated by a bond (more generally, a binding interaction) between the enzyme and the substrate.〔 His work was taken up by German biochemist Leonor Michaelis and Canadian physician Maud Menten, who investigated the kinetics of an enzymatic reaction mechanism, invertase, that catalyzes the hydrolysis of sucrose into glucose and fructose.〔 In 1913, they proposed a mathematical model of the reaction.〔 It involves an enzyme E binding to a substrate S to form a complex ES, which in turn is converted into a product P and the enzyme. This may be represented schematically as
:
E + S \, \overset \, ES \, \overset \, E + P

where k_f, k_r, and k_\mathrm denote the rate constants,〔 and the double arrows between S and ES represent the fact that enzyme-substrate binding is a reversible process.
Under certain assumptions – such as the enzyme concentration being much less than the substrate concentration – the rate of product formation is given by
:v = \frac = V_\max \frac = k_\mathrm ()_0 \frac .
The reaction rate increases with increasing substrate concentration (), asymptotically approaching its maximum rate V_\max, attained when all enzyme is bound to substrate. It also follows that V_\max = k_\mathrm ()_0, where ()_0 is the initial enzyme concentration. k_\mathrm, the turnover number, is the maximum number of substrate molecules converted to product per enzyme molecule per second.
The Michaelis constant K_\mathrm is the substrate concentration at which the reaction rate is at half-maximum,〔 and is an inverse measure of the substrate's affinity for the enzyme—as a small K_\mathrm indicates high affinity, meaning that the rate will approach V_\max more quickly.〔 The value of K_\mathrm is dependent on both the enzyme and the substrate, as well as conditions such as temperature and pH.
The model is used in a variety of biochemical situations other than enzyme-substrate interaction, including antigen-antibody binding, DNA-DNA hybridization, and protein-protein interaction.〔〔 It can be used to characterise a generic biochemical reaction, in the same way that the Langmuir equation can be used to model generic adsorption of biomolecular species.〔 When an empirical equation of this form is applied to microbial growth, it is sometimes called a Monod equation.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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