Km (Michaelis constant)
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- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
(k_{-1}+k_cat)/k_1About this calculator
The Michaelis constant (Km) calculator determines an enzyme's affinity for its substrate using the formula Km = (k₋₁ + k_cat) / k₁, where k₋₁ is the reverse rate constant, k_cat is the catalytic rate constant, and k₁ is the initial association constant.
This calculation is crucial in enzymatic kinetics studies, helping to understand enzyme-substrate interactions. Lower Km values indicate higher enzyme-substrate affinity, while higher values suggest lower specificity.
Use this tool in inhibitor studies, drug development, or biochemical kinetics. Caution: k₋₁, k_cat, and k₁ measurements must be taken under controlled conditions to ensure accurate results.
The calculator also allows comparisons between enzymes or variants, assessing catalytic efficiency in experimental contexts.
Frequently asked questions
What are the common units for Km?
Km is typically expressed in molarity (M) or millimolarity (mM), depending on the substrate concentration in the experiment.
How does temperature affect the Km value?
Temperature influences enzymatic activity: moderate increases may lower Km, but excessively high temperatures can denature the enzyme, altering its value.
What is the difference between Km and the dissociation constant (Kd)?
Km measures affinity under catalytic conditions, while Kd describes enzyme-substrate binding at equilibrium, without chemical reaction.
What are typical Km values for common enzymes?
Typical values range from micromolar (µM) to millimolar (mM), depending on the enzyme and substrate. For example, lactate dehydrogenase has a Km around 0.1 mM.
How can this calculator be used in inhibitor studies?
By calculating Km with and without inhibitors, it is possible to determine the type of inhibition (competitive, non-competitive) and the inhibitor's efficacy in reducing enzymatic activity.