Michaelis–Menten enzyme kinetics
About this app
Explore substrate saturation, Vmax and Km, with a Lineweaver–Burk plot. Compare competitive and noncompetitive inhibition.
The Michaelis–Menten equation
For simple enzymes the rate of an enzyme-catalysed reaction follows v = Vmax · [S] / (Km + [S]). At low substrate concentration [S], v rises almost linearly; at high [S], v approaches the maximum Vmax because all enzymes are occupied (saturation). Km is the substrate concentration at which v reaches exactly ½ Vmax; a small Km means high affinity. A competitive inhibitor competes with the substrate for the active site and raises the apparent Km while Vmax stays the same. A noncompetitive inhibitor lowers Vmax while Km stays the same.
What the app shows
The v–[S] plot shows the Michaelis–Menten curve with the Vmax asymptote, ½ Vmax and a Km marker, plus the current operating point. Next to it the Lineweaver–Burk plot shows 1/v against 1/[S] as a straight line with slope Km/Vmax, y-intercept 1/Vmax and x-intercept −1/Km. A readout gives v, effective Vmax and Km and the share of occupied enzymes.
Things to try
Raise the substrate concentration and watch enzyme occupancy approach 100 % while v hardly increases any more. Switch on competitive inhibition: the curve flattens, the Km marker moves right, and the Lineweaver–Burk line gets steeper but meets the y-axis at the same point. Compare with noncompetitive inhibition, where the x-intercept stays the same.
Frequently asked questions
- What does the Michaelis constant Km tell you?
- Km is the substrate concentration at which an enzyme reaches half its maximum rate. It is a measure of affinity: a small Km means little substrate is enough for a high rate. Km has the unit of a concentration, for example mmol/L.
- What is the difference between competitive and noncompetitive inhibition?
- A competitive inhibitor binds the active site and competes with the substrate; plenty of substrate can outcompete it. So the apparent Km rises while Vmax can still be reached. A noncompetitive inhibitor binds elsewhere and takes part of the enzyme out of action; Vmax falls and Km stays the same.
- What is the Lineweaver–Burk plot used for?
- The Lineweaver–Burk plot graphs 1/v against 1/[S] and turns the saturation curve into a straight line. The y-intercept gives 1/Vmax, the x-intercept −1/Km. The type of inhibition can be read from which intercept changes.
- What can I adjust in the Enzyme Kinetics app?
- You set substrate concentration, Vmax and Km and switch on competitive or noncompetitive inhibition, or both at once. With inhibition on, both plots show a comparison curve without inhibition. A readout shows the rate, the effective parameters and enzyme occupancy.
Subject: Biology (Gymnasium)
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