substratsaffinitetskonstanten

The substratsaffinitetskonstanten, also known as the substrate affinity constant, is a parameter that quantifies the binding affinity between an enzyme and its substrate. It is commonly denoted as the Michaelis constant (Km) in enzyme kinetics. The value of Km is defined as the substrate concentration at which the reaction velocity reaches half of its maximum (Vmax). A lower Km indicates a higher affinity because less substrate is required to achieve a given rate of reaction, while a higher Km denotes a weaker affinity.

The substratsaffinitetskonstanten is derived from the Michaelis–Menten equation V = (Vmax[S])/(Km + [S]) and arises from the steady‑state approximation that the concentration of the enzyme–substrate complex remains relatively constant during the reaction. It can be interpreted as an equilibrium dissociation constant (Kd) for the formation of the enzyme–substrate complex in the absence of product formation, making it a useful measure of how tightly an enzyme binds its substrate.

Experimental determination of the substratsaffinitetskonstanten usually involves measuring initial reaction rates at varying substrate concentrations and fitting the data to the Michaelis–Menten model or using Lineweaver–Burk plots. Typical values range from nanomolar to micromolar for high‑affinity enzymes, but can be in the millimolar range for enzymes with low substrate affinity.

The substratsaffinitetskonstanten is distinct from kinetic parameters such as the turnover number (kcat) or catalytic efficiency (kcat/Km). While kcat describes how rapidly an enzyme converts substrate to product once bound, the substratsaffinitetskonstanten reflects the binding step itself. These parameters together provide a comprehensive picture of enzyme efficiency and are crucial in fields such as drug design, metabolic engineering, and biochemistry.