Enzyme Kinetics Lab

How to use it

1. Move the Vmax and Km sliders and watch the curve. The dashed lines mark Vmax and the substrate level that gives half of Vmax, which is Km.
2. Choose an inhibitor and raise [I]. The faint dashed curve shows the reaction without the inhibitor, so you can compare.
3. Switch the graph to Lineweaver–Burk to see why each inhibitor type leaves a different fingerprint.
4. Press Run an experiment to collect eight noisy measurements, estimate Km and Vmax from them, then check your answer.

Try this

1. With no inhibitor, set Km to 5 mM. What rate do you get at [S] = 5 mM? Why is it exactly half of Vmax?
2. Add a competitive inhibitor at [I] = 4 mM. Which constant changes, and which stays the same? How does the Lineweaver–Burk line move?
3. Repeat with a non-competitive and then an uncompetitive inhibitor. Describe each fingerprint in one sentence.
4. Run an experiment and estimate the apparent Km and Vmax to within 10%.

The science

The Michaelis–Menten equation is v = Vmax·[S] / (Km + [S]). Vmax is the maximum rate when the enzyme is saturated; Km is the substrate concentration at which the rate is half of Vmax.

A competitive inhibitor competes with the substrate for the active site, so more substrate can overcome it: the apparent Km rises (Km × (1 + [I]/Ki)) while Vmax stays the same.

A pure non-competitive inhibitor binds elsewhere and lowers the apparent Vmax (Vmax ÷ (1 + [I]/Ki)) without changing Km. An uncompetitive inhibitor binds only the enzyme–substrate complex and lowers both Vmax and Km by the same factor.

In the lab model, measurements carry about ±3% random error, like a real assay. Real enzymes can also show cooperativity or substrate inhibition, which this simple model leaves out.