MichaelisMentenkinetiek

Michaelis-Menten kinetics is a model that describes the rate of many enzyme-catalyzed reactions, particularly those involving a single substrate turning into product. The model centers on the formation of an enzyme-substrate complex (ES) and its subsequent breakdown to enzyme and product. It provides a simple framework to relate reaction rate to substrate concentration under steady, controlled conditions.

The core equation is v = (Vmax [S])/(Km + [S]), where v is the initial reaction rate, [S] is substrate concentration, Vmax is the maximum rate achieved when the enzyme is saturated with substrate, and Km is the Michaelis constant. Vmax equals kcat [E]tot, with kcat being the turnover number (the number of catalytic cycles per enzyme molecule per unit time) and [E]tot the total enzyme concentration. Km is the substrate concentration at which v is half of Vmax and is often interpreted as a measure of the enzyme’s affinity for the substrate, though it also depends on reaction conditions such as pH and temperature.

The model relies on certain assumptions: a steady-state balance for ES (the Briggs-Haldane approach), a single substrate, a simple one-step catalytic mechanism, and constant [E]tot measured under initial-rate conditions. It has limitations; it may not apply to allosteric enzymes, multi-substrate reactions, substrate inhibition, or reactions with significant conformational changes or dynamic equilibria.

Historically, the model was introduced by Michaelis and Menten in 1913 and has become a foundational tool in biochemistry and pharmacology for estimating kinetic parameters, comparing enzymes, and assessing catalytic efficiency through kcat and Km (and the ratio kcat/Km).