Calculator Inputs
Formula used
The calculator supports several common enzyme kinetic models, then derives useful summaries such as saturation, apparent constants, reciprocal coordinates, kcat, and estimated product formation.
| Model | Velocity equation | Interpretation |
|---|---|---|
| Michaelis-Menten | v = (Vmax × [S]) / (Km + [S]) | Basic saturation behavior with no inhibitor. |
| Competitive inhibition | v = (Vmax × [S]) / (αKm + [S]) | Only apparent Km increases, where α = 1 + [I]/Ki. |
| Uncompetitive inhibition | v = (Vmax × [S]) / (Km + α′[S]) | Both apparent Km and Vmax decrease, with α′ = 1 + [I]/Ki′. |
| Noncompetitive inhibition | v = (Vmax × [S]) / (αKm + α[S]) | Apparent Vmax falls while apparent Km stays constant. |
| Mixed inhibition | v = (Vmax × [S]) / (αKm + α′[S]) | Both apparent constants change by different amounts. |
| Substrate inhibition | v = (Vmax × [S]) / (Km + [S] + [S]²/Ksi) | Rate drops at very high substrate concentrations. |
| Hill cooperativity | v = Vmax × [S]n / (K0.5n + [S]n) | Useful for cooperative binding rather than classic hyperbolic kinetics. |
Additional outputs use straightforward relationships: saturation = v / apparent Vmax, kcat = Vmax / [E], catalytic efficiency = kcat / Km, and product ≈ v × time for an initial-rate estimate.
How to use this calculator
- Enter substrate concentration, Vmax, and Km or K0.5.
- Select the kinetic model that matches your system.
- Add inhibitor constants, Hill coefficient, or enzyme concentration when needed.
- Provide a substrate range to build a kinetic profile table.
- Submit the form to show results directly below the header.
- Review velocity, apparent constants, saturation, kcat, and generated reciprocal values.
- Download the summary as CSV or export a PDF version.
Example data table
Example below uses Michaelis-Menten kinetics with Vmax = 120.00 µmol/min and Km = 2.50 mM.
| [S] (mM) | Velocity (µmol/min) | Saturation (%) |
|---|---|---|
| 0.50 | 20.00 | 16.67 |
| 1.00 | 34.29 | 28.57 |
| 2.00 | 53.33 | 44.44 |
| 5.00 | 80.00 | 66.67 |
| 10.00 | 96.00 | 80.00 |
Frequently asked questions
1. What does enzyme velocity mean here?
It is the predicted initial reaction rate at the chosen substrate concentration and kinetic model. The calculator estimates how fast product forms before significant depletion or reverse effects appear.
2. When should I use the competitive inhibition model?
Use it when the inhibitor competes with substrate for the active site. In this case, apparent Km increases, but the maximum possible rate remains unchanged.
3. Why does the calculator show apparent constants?
Apparent values describe how inhibition or cooperativity changes the observed kinetic behavior. They help compare experimental conditions without changing the original baseline constants entered by the user.
4. What is the purpose of the Hill coefficient?
The Hill coefficient measures cooperativity. A value near one suggests little cooperative behavior, values above one suggest positive cooperativity, and values below one suggest negative cooperativity.
5. How is product formed estimated?
The tool multiplies the calculated initial rate by the entered reaction time. This is most useful for short durations where the initial-rate assumption remains reasonable.
6. Why are reciprocal values included?
Reciprocal values, 1/[S] and 1/v, are useful for Lineweaver-Burk style inspection. They can help visualize shifts in slope and intercept across inhibition models.
7. What happens if enzyme concentration is left empty?
Velocity still calculates normally. Only turnover-based outputs such as kcat and catalytic efficiency depend on enzyme concentration, so those results appear as unavailable.
8. Can this replace full experimental fitting?
No. It is a helpful educational and planning tool, but rigorous kinetic studies should still use carefully collected data, regression fitting, and appropriate mechanistic validation.