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Michaelis-Menten kinetics

Michaelis-Menten kinetics fits y = Vmax · x / (Km + x), the standard model for single-site enzyme kinetics.

What is Michaelis-Menten kinetics?

Two parameters: Vmax (asymptotic maximum rate, reached at saturating substrate) and Km (the substrate concentration at which y = Vmax/2 — a measure of enzyme-substrate affinity, with smaller Km meaning higher affinity).

Linearisations (Lineweaver-Burk, Eadie-Hofstee, Hanes-Woolf) are mostly of historical interest — they invert the data in ways that distort the error structure and bias the fit. Direct nonlinear fitting (what this test does) is the modern standard.

When should I use Michaelis-Menten kinetics?

  • Single-site enzyme kinetics.
  • Any saturating substrate-velocity relationship without cooperativity.

What data does it need?

Numeric [substrate] + velocity.

What does it report?

Vmax + Km with 95% CIs.

What does it assume?

  • Single-site kinetics (no cooperativity).
  • Substrate spans both linear (x ≪ Km) and saturated (x ≫ Km) regions for identifiability.

How do I interpret the result?

If the fitted Vmax CI is enormous, the substrate range didn't reach saturation — add higher-concentration points to identify Vmax.

See also

References

  • Michaelis & Menten (1913). Die Kinetik der Invertinwirkung. Biochem. Z. 49.