PHARM/PCS V5 · Procedure 18
Enzyme Kinetics I: Michaelis-Menten Equation
Estimate Vmax and KM from initial-velocity data across substrate concentrations, using the Lineweaver-Burk double-reciprocal fit.
What it computes
Fits the Michaelis-Menten equation via the Lineweaver-Burk linearization (1/v vs. 1/[S]) and reports Vmax and KM.
Inputs and outputs
You provide
- Substrate concentration and velocity, one pair per line
PHARM/PCS reports
- The fitted Lineweaver-Burk line, slope and intercept
- Vmax
- KM
- The Lineweaver-Burk plot
When to use it
To get Vmax and KM for an enzyme from initial-velocity data across substrate concentrations, the baseline characterization before you probe inhibitors with Procedures 19 (competitive) and 20 (noncompetitive).
Reading the results
The double-reciprocal transform is convenient but compresses high-substrate points and stretches low-substrate ones, so the fit is disproportionately swayed by measurements at low [S], where relative error is largest. Take the numbers as solid estimates, but be skeptical if one or two low-[S] points are driving the whole line.
About the method
This procedure uses the Lineweaver-Burk linearization the textbook uses, and reproduces the book's output to at least six significant figures. Current practice often prefers direct nonlinear fitting, or the Eadie-Hofstee or Hanes-Woolf forms, because the double-reciprocal transform weights low-substrate points heavily. The procedure stays with Lineweaver-Burk for fidelity to the text.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.