MichaelisMenten

Michaelis-Menten kinetics, named after Leonor Michaelis and Maud Menten, is a mathematical model of the rate of enzymatic reactions. It describes how the reaction velocity v depends on substrate concentration [S] under conditions where the formation and breakdown of the enzyme-substrate complex reach a steady state. The rate is given by v = (Vmax [S]) / (Km + [S]), where Vmax is the maximum rate achieved at saturating substrate, and Km is the Michaelis constant, the substrate concentration at which v is half of Vmax. Km is a composite parameter reflecting both substrate binding affinity and catalytic turnover, and it is commonly interpreted as an indicator of enzyme-substrate affinity, with lower Km indicating higher affinity in simple scenarios.

The model assumes a single substrate, a single productive enzyme-substrate complex, initial rate measurement, constant total enzyme concentration [E]t, and that [S] changes little during the initial phase. It can be derived from a rapid equilibrium or steady-state assumption. In practice, Km and Vmax are obtained by fitting experimental rate data to the equation.

Applications and limitations: It is widely used to characterize enzyme kinetics, estimate catalytic efficiency (kcat/Km) when kcat is known, and compare enzyme variants. It is most accurate at low product accumulation and near the initial rate; it may fail for allosteric enzymes, multi-substrate reactions, or significant product inhibition. Extensions include mechanisms for multiple substrates, inhibition, and more complex rate laws; kcat and catalytic efficiency provide a normalized view of enzyme performance.