Michaelis constant

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Michaelis constant is the substrate concentration at which the reaction velocity is equal to half the maximal velocity of the reaction.

Km = Michaelis constant

Km = the value of substrate concentration[S] that causes V= ½ Vmax *

The units of Km are M, concentration.

Km indicates the affinity of the enzyme for its substrate and thus the stability of the Enzyme-Substrate Complex.

Velocity is related to Km through the Michaelis & Menten equation: v = (Vmax [S])/(Km + [S]).

Vmax = maximum rate of reaction achievable for the enzyme under given conditions, only occurs at infinite substrate concentration.

[S] = substrate concentration.

A reaction with a low Michaelis constant value indicates a low binding affinity, whereas a large value indicates a high binding affinity[1].


  1. Michaelis, L; Menten, ML; Johnson, KA; Goody, R S. The original Michaelis constant: translation of the 1913 Michaelis-Menten paper, Biochemistry, 04 October 2011, Vol.50(39), pp.8264-9
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