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Guilherme Mazui

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What is the Difference Between Kd and Km?

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The main difference between Kd and Km lies in their definitions and the properties they describe in enzymatic reactions:

  1. Kd (Dissociation Constant):
  • Kd is a thermodynamic constant.
  • It represents the affinity of a substrate towards an enzyme.
  • A lower Kd indicates a stronger binding affinity between the enzyme and the substrate.
  • Kd is calculated as the ratio of the concentrations of free enzyme (E) and free substrate (S) divided by the concentration of the enzyme-substrate complex (ES).
  1. Km (Michaelis Constant):
  • Km is a kinetic constant, not a thermodynamic constant.
  • It represents the relationship between substrate concentration and reaction speed.
  • A lower Km means that the enzyme has a stronger affinity for the substrate and requires a lower substrate concentration to reach its maximum reaction speed (Vmax).
  • Km is related to the concentration of substrate at which the enzyme is half-saturated (Vmax/2).

In summary, Kd is a thermodynamic constant that describes the binding affinity between an enzyme and its substrate, while Km is a kinetic constant that represents the relationship between substrate concentration and reaction speed.

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  • What is the Difference Between Kd and Km?
  • Comparative Table: Kd vs Km

    • Comparative Table: Kd vs Km

    The main difference between Kd and Km lies in their nature and the information they provide about enzymatic reactions. Here is a table summarizing the differences between Kd and Km:

    Property Kd (Dissociation Constant) Km (Michaelis Constant)
    Nature Thermodynamic constant Kinetic constant
    Role Represents the affinity of a substrate towards an enzyme Represents the relationship between substrate concentration and reaction speed
    Affinity Lower Kd means higher affinity, and higher Kd means lower affinity Lower Km means higher affinity, and higher Km means lower affinity
    Formation Kd = [A][B] / [AB] Km = [E] at 1/2 Vmax
    Relationship The ratio Km/Kd can approximate binding affinity, but assuming they are equivalent is a common and problematic fallacy Km is related to Kd, and higher Km generally indicates a higher Kd

    In summary, Kd represents the affinity of a substrate towards an enzyme and is a thermodynamic constant, while Km represents the relationship between substrate concentration and reaction speed, and it is a kinetic constant.

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    Guilherme Mazui

    Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.