Michaelis Constant

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Michaelis constant

[mi′kā·ləs ‚kän·stənt]
A constant Km such that the initial rate of reaction V, produced by an enzyme when the substrate concentration is high enough to saturate the enzyme, is related to the rate of reaction v at a lower substrate concentration c by the formula V = v (1 + Km / c).

Michaelis Constant


one of the most important parameters of enzyme kinetics, characterizing the dependence of the rate of an enzyme process on the substrate concentration; derived by the German scientists L. Michaelis and M. Menten in 1913.

According to the Michaelis-Menten theory, the first step in any enzyme process is a reversible reaction between the enzyme (E) and the substrate (S), leading to the formation of an intermediate enzyme-substrate complex (£5), which then undergoes practically irreversible decomposition, yielding a reaction product (P) and the original enzyme (E):

The reactions for the formation and decomposition of the ES complex are characterized by the rate constants k\, £_i , and k 2. If the substrate concentration markedly exceeds the enzyme concentration ([5] » [E]), so that the ES concentration becomes constant, then the rate of the enzyme reaction (v) is given by the equation

where V is the maximum rate of the reaction, achieved at full saturation of the enzyme by the substrate. The ratio of the rate constants (k-\+ki)/k\ is the Michaelis constant (km).

When the Michaelis constant is substituted into equation (2), the Michaelis-Menten equation is obtained:

It follows from equation (3) that the Michaelis constant is numerically equal to the substrate concentration at which the reaction rate reaches half its maximum possible value (see Figure

Figure 1. Ratio of enzyme reaction rate (v) to substrate concentration [S]

In a number of cases, in which ki is negligible, the Michaelis constant becomes equivalent to k\/k \ and may serve as a measure of the affinity of the substrate for the enzyme.

The Michaelis constant is given in units of concentration. In practice, the value for the Michaelis constant is found graphically using the ratio of the enzyme reaction rate to the substrate concentration.


lakovlev, V. A. Kinetika fermentativnogo kataliza. Moscow, 1965.
Webb, L. Ingibitory fermentov i metabolizma. Moscow, 1966. (Translated from English.)


References in periodicals archive ?
Michaelis-Menten kinetics describes the rate of enzymatic reactions.
Caption: Figure 1: (a) Absorption spectra of the TvL, CA, and CAQ; (b) absorbance as a function of time for the oxidation reaction of different CA concentrations ([lambda] = 410 nm); (c) spectrophotometric determination of the Michaelis-Menten kinetics for CA oxidation by TvL; (d) spectrophotometric determination of the Michaelis-Menten kinetics for GA and CT oxidation by TvL.
The kinetics of PPO in the presence of D-ISO does not fit a typical Michaelis-Menten kinetics, since it shows an asymptotic behavior on the abscissa, corresponding to a total or linear inhibition (Fersh, 1985), because the slope is equal to zero, as well as Km/Vmax.
The effect of the drug is considered with Michaelis-Menten kinetics, and we use mixed-order pharmacokinetic model to describe the depletion of the drug.
Kinetic profiling revealed that formation of icaritin-3-O-glucuronide (M13) and icaritin-7-O-glucuronide (M18) in RLM was well modeled by the substrate inhibition equation (Figure 3(a)), whereas they followed the classical Michaelis-Menten kinetics in RIM (Figure 3(b)).
The first term shows a growing rate stimulated by IFN-[gamma] which follows a Michaelis-Menten Kinetics with maximal effect [mathematical expression not reproducible] and Michaelis parameter [mathematical expression not reproducible].
The rates followed typical Michaelis-Menten kinetics for both sulfopyruvate ([K.sub.M] 196 [micro]M) and NADH ([K.sub.M] 55.1 [micro]M) with the sulfopyruvate value being 5-fold that found for M.
The apparent Michaelis-Menten kinetics are [K.sub.rn] = 0.29mol/L and apparent [V.sub.max] = 0.563 mmol/L-h for flurbiprofen.
Inhibition of ureases by compounds 1c-10c is not time dependent and is perfectly fixed to Michaelis-Menten kinetics. These experiments demonstrated that both ureases were strongly inhibited by studied vanadium complexes 1c-10c.
The basic of kinetics of ammonium and nitrite oxidation was calculated with Michaelis-Menten kinetics equation using the Lineweaver-Burk plots [37].
Arthurs, "Complementary variational principles for diffusion problems with Michaelis-Menten kinetics," Bulletin of Mathematical Biology, vol.
Michaelis-Menten Kinetics. Since the rate was fractional-order in [[TCH].sub.o], Michaelis-Menten type of kinetics [13] was adopted.