Model enzyme rates with inhibitor effects in seconds. Compare competitive, uncompetitive, mixed, and noncompetitive cases. Export results, verify units, and learn kinetics easily today.
This calculator uses Michaelis–Menten kinetics with common inhibition models. It treats inhibitor effects through α and α′.
Sample values illustrate how velocity drops under inhibition. Units are arbitrary and should be treated as placeholders.
| Model | Vmax | Km | [S] | [I] | Ki | Ki′ | v |
|---|---|---|---|---|---|---|---|
| Baseline | 120 | 15 | 10 | 0 | – | – | 48 |
| Competitive | 120 | 15 | 10 | 5 | 8 | – | 34.91 |
| Uncompetitive | 120 | 15 | 10 | 5 | – | 20 | 43.64 |
| Noncompetitive | 120 | 15 | 10 | 5 | 8 | 8 | 29.54 |
| Mixed | 120 | 15 | 10 | 5 | 8 | 20 | 32.54 |
This tool estimates the initial reaction velocity (v) for an enzyme-catalyzed process in the presence of an inhibitor. It uses the standard Michaelis–Menten framework and expresses inhibition through the scaling factors α and α′, which depend on inhibitor level and inhibition constants. The output includes v, plus apparent parameters that help compare conditions.
The example inputs are Vmax = 120, Km = 15, [S] = 10, and [I] = 5 (concentration units are user-defined). Baseline velocity is 48. With Ki = 8 (competitive), α = 1 + 5/8 = 1.625 and the velocity drops to about 34.91.
Competitive inhibition increases the apparent Km while keeping Vmax unchanged, shifting the curve rightward. Uncompetitive inhibition reduces both Km and Vmax by the same factor. Pure noncompetitive inhibition reduces Vmax without changing Km. Mixed inhibition can change both, producing intermediate behavior.
The calculator provides Vmax(app) and Km(app) so you can summarize inhibition compactly. In the example, competitive inhibition yields Km(app) = α·Km = 24.38 (approx.), while keeping Vmax(app) = 120. For mixed inhibition with Ki′ = 20, Vmax(app) = Vmax/α′ = 96 and Km(app) ≈ 19.50.
A single-point velocity is useful, but experimental interpretation often needs a full substrate-response profile. The series table computes velocity over a user-selected [S] range while holding [I] fixed. This lets you compare shifts in curvature, estimate practical working ranges, and prepare plots in external software using the CSV export.
The mathematics is unit-agnostic, but values must share consistent concentration units. If Km is entered in mM, then [S], [I], Ki, and Ki′ should also be in mM. Rate units are labels only; scaling errors typically come from mixed concentration units, not from the display selectors.
Validate that Vmax and Km are positive and that concentrations are non-negative. If inhibitor is present but an inhibition constant is missing, the model may underrepresent inhibition. Compare baseline versus inhibited outputs at the same [S] to confirm the expected direction of change.
Use the on-page PDF for quick documentation and the CSV for detailed analysis. CSV includes inputs, single-point results, and the full series table (up to 250 rows), which supports reproducible reporting. For publications, consider fitting multiple inhibitor levels and comparing how Km(app) and Vmax(app) vary with [I].
Ki describes inhibitor affinity for free enzyme. Ki′ describes inhibitor affinity for the enzyme–substrate complex. Smaller values indicate stronger binding. Use consistent concentration units across all inputs.
Competitive inhibitors reduce effective substrate binding by raising the apparent Km. At very high substrate, the inhibitor can be outcompeted, so the maximum achievable rate remains close to Vmax.
Select mixed inhibition when the inhibitor affects both free enzyme and the ES complex, so both Ki and Ki′ are relevant. If one pathway dominates, mixed naturally approximates competitive or uncompetitive behavior.
When [I] = 0, α = α′ = 1. The equation reduces to baseline Michaelis–Menten kinetics, and apparent parameters match the original Vmax and Km.
NaN typically occurs if inputs are non-numeric or if parameters create an invalid denominator. Confirm positive Vmax and Km, non-negative concentrations, and that required inhibition constants are provided when inhibitor is present.
No. Unit selectors only change displayed labels. Calculations use the numeric values you enter. Correctness depends on you keeping Km, [S], [I], Ki, and Ki′ in the same concentration units.
Use CSV for plotting, regression, and archiving the full series table. Use the PDF for quick sharing or attaching a summary to lab notes or reports.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.