Michaelis Constant

Michaelis constant

[mi′kā·ləs ‚kän·stənt] (biochemistry) A constant K_msuch 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 + K_m/ 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.

REFERENCES

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

D. M. BELEN’KII

Michaelis constant

Mi·chae·lis con·stant

(mi-kā'lis), 1. the true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction (usually symbolized by K_s); 2. the concentration of the substrate at which half the true maximum velocity of an enzyme-catalyzed reaction is achieved (when velocities are measured under initial rate and steady-state conditions); the ratio of rate constants (k₂ + k₃)/k₁ in the single-substrate enzyme-catalyzed reaction: E + S ⇄ ES ⇄ E + products, where E represents the free enzyme, S is the substrate, and ES is the central binary complex. The expression for the Michaelis constant will be more complex for multisubstrate reactions. An apparent Michaelis constant is a constant determined either under conditions that are not strictly steady-state and initial rate or under a condition that varies with the concentration of one or more cosubstrates. Synonym(s): Michaelis-Menten constant [Leonor Michaelis]

Mi·chae·lis con·stant

(mi-kā'lis kon'stănt) 1. The true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction (usually symbolized by K_s). 2. The concentration of the substrate at which half the true maximum velocity of an enzyme-catalyzed reaction is achieved. [Leonor Michaelis]

Michaelis,

Leonor, German-U.S. chemist and physician, 1875-1949. Michaelis bufferMichaelis constant - the true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction. Synonym(s): Michaelis-Menten constantMichaelis-Gutmann body - a rounded homogenous body containing calcium and iron found within macrophages in the bladder wall in malacoplakia.Michaelis-Menten constant - Synonym(s): Michaelis constantMichaelis-Menten equation - an initial-rate equation for a single-substrate noncooperative enzyme-catalyzed reaction relating the initial velocity to the initial substrate concentration. Synonym(s): Victor-Michaelis-Menten equationMichaelis-Menten hypothesis - that a complex is formed between an enzyme and its substrate (the O'Sullivan-Tompson hypothesis), which complex then decomposes to yield free enzyme and the reaction products (Brown hypothesis), the latter rate determining the overall rate of substrate-product conversion.Victor-Michaelis-Menten equation - Synonym(s): Michaelis-Menten equation

单词	michaelis constant
释义	DictionarySeeconstant Michaelis Constant Michaelis constant [mi′kā·ləs ‚kän·stənt] (biochemistry) A constant K_msuch 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 + K_m/ 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. REFERENCES lakovlev, V. A. Kinetika fermentativnogo kataliza. Moscow, 1965. Webb, L. Ingibitory fermentov i metabolizma. Moscow, 1966. (Translated from English.) D. M. BELEN’KII Michaelis constant Mi·chae·lis con·stant (mi-kā'lis), 1. the true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction (usually symbolized by K_s); 2. the concentration of the substrate at which half the true maximum velocity of an enzyme-catalyzed reaction is achieved (when velocities are measured under initial rate and steady-state conditions); the ratio of rate constants (k₂ + k₃)/k₁ in the single-substrate enzyme-catalyzed reaction: E + S ⇄ ES ⇄ E + products, where E represents the free enzyme, S is the substrate, and ES is the central binary complex. The expression for the Michaelis constant will be more complex for multisubstrate reactions. An apparent Michaelis constant is a constant determined either under conditions that are not strictly steady-state and initial rate or under a condition that varies with the concentration of one or more cosubstrates. Synonym(s): Michaelis-Menten constant [Leonor Michaelis] Mi·chae·lis con·stant (mi-kā'lis kon'stănt) 1. The true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction (usually symbolized by K_s). 2. The concentration of the substrate at which half the true maximum velocity of an enzyme-catalyzed reaction is achieved. [Leonor Michaelis] Michaelis, Leonor, German-U.S. chemist and physician, 1875-1949. Michaelis bufferMichaelis constant - the true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction. Synonym(s): Michaelis-Menten constantMichaelis-Gutmann body - a rounded homogenous body containing calcium and iron found within macrophages in the bladder wall in malacoplakia.Michaelis-Menten constant - Synonym(s): Michaelis constantMichaelis-Menten equation - an initial-rate equation for a single-substrate noncooperative enzyme-catalyzed reaction relating the initial velocity to the initial substrate concentration. Synonym(s): Victor-Michaelis-Menten equationMichaelis-Menten hypothesis - that a complex is formed between an enzyme and its substrate (the O'Sullivan-Tompson hypothesis), which complex then decomposes to yield free enzyme and the reaction products (Brown hypothesis), the latter rate determining the overall rate of substrate-product conversion.Victor-Michaelis-Menten equation - Synonym(s): Michaelis-Menten equation
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