Michaelis Constant (Km) Calculator

The Michaelis constant (Km) is a fundamental parameter in enzyme kinetics that represents the substrate concentration at which the reaction rate is half of its maximum value (Vmax). A lower Km indicates higher enzyme affinity for its substrate.

Km can be calculated from rate constants using the formula: Km = (k₋₁ + k₂) / k₁, where k₁ is the substrate binding rate, k₋₁ is the unbinding rate, and k₂ is the product formation rate.

When you have kinetic data, Km can be calculated using: Km = (Vmax × [S] / V₀) - [S], where Vmax is the maximum reaction rate, [S] is substrate concentration, and V₀ is the initial velocity.

A high Km value indicates low enzyme affinity for the substrate, meaning a higher substrate concentration is needed to reach half-maximal velocity. This suggests weaker enzyme-substrate binding.

A low Km value indicates high enzyme affinity for the substrate, meaning the enzyme can achieve half-maximal velocity at low substrate concentrations. This suggests strong enzyme-substrate binding.

Km is the Michaelis constant related to enzyme kinetics, while Kd is the dissociation constant for equilibrium binding. Km equals Kd only when k₂ << k₋₁ (rapid equilibrium assumption).

Km is typically expressed in concentration units such as μM (micromolar), mM (millimolar), or M (molar), depending on the substrate concentration range in the experiment.

Enzyme efficiency is measured by the kcat/Km ratio, also called the specificity constant. Higher kcat/Km values indicate more efficient enzymes, with the theoretical maximum being around 10⁸-10⁹ M⁻¹s⁻¹.