Enzyme Kinetics Simulator
Michaelis–Menten, and how inhibitors give themselves away
Tune Vmax, Km, and inhibitor concentration across four inhibition mechanisms, and watch each one produce its own unmistakable signature on a Lineweaver–Burk plot.
The takeaway
You can determine where a drug binds without ever seeing it bind, the geometry of the double-reciprocal plot tells you the mechanism.
Inhibition mechanism
Km apparent
150.0µM
↑ 3.00× vs 50
Vmax apparent
100.0µM/min
= 100% of Vmax
kcat (turnover)
166.7s⁻¹
1.00e+4 substrates · enzyme⁻¹ · min⁻¹
kcat / Km
1.11 × 10⁶M⁻¹s⁻¹
specificity constant
Michaelis–Menten curve
v = Vmax·[S] / (Km + [S])The hyperbola saturates: once every active site is occupied, more substrate buys you nothing. The dashed grey line is the uninhibited reference, the difference between the two curves is the drug's effect.
Inhibition at [S] = Km
50.0%
Surmountable by [S]?
Yes, Vmax recoverable
Intrinsic kcat
166.7 s⁻¹
Lineweaver–Burk (double reciprocal)
1/v = (Km/Vmax)·(1/[S]) + 1/VmaxLinearise the hyperbola and each mechanism leaves a different fingerprint. Watch where the lines cross as you raise [I], that intersection point is the whole diagnosis.
| Condition | Slope (Km/Vmax) | y-int (1/Vmax) | x-int (−1/Km) |
|---|---|---|---|
| [I] = 0 | 0.500 | 0.0100 | -0.0200 |
| [I] = 20 µM | 1.500 | 0.0100 | -6.67e-3 |
| [I] = 40 µM | 2.500 | 0.0100 | -4.00e-3 |
Competitive signature: Lines share the SAME y-intercept (1/Vmax is untouched) and fan out to different x-intercepts. A shared y-intercept is the fingerprint of competitive inhibition.
Mechanism · Competitive
Where does the inhibitor bind? Free enzyme (E) only, the active site
The inhibitor is a substrate look-alike that occupies the active site of the FREE enzyme. Enzyme and inhibitor compete for the same real estate, so the enzyme merely looks like it has lost affinity, apparent Km rises. Flood the system with substrate and you out-compete the inhibitor: Vmax is fully recoverable. This surmountability is the diagnostic hallmark.
Effect on Km
Km apparent ↑ by α
Effect on Vmax
Vmax unchanged
In the clinic: Methotrexate on dihydrofolate reductase (a folate mimic) and statins on HMG-CoA reductase (an HMG-CoA mimic). Both are active-site rivals.
Why pharma cares
Mechanism of action is not a marketing word, it is a measurement. You run the assay at several [S] and several [I], plot the double reciprocal, and the geometry of the lines tells you whether your molecule sits in the active site or somewhere else entirely.
- →Competitive drugs lose potency when the natural substrate piles up. A competitive kinase inhibitor fights millimolar cellular ATP, which is why cellular IC50 often sits far above the biochemical one.
- →Uncompetitive drugs get stronger where flux is highest, self-targeting overactive tissue. That selectivity is a design goal, not an accident.
- →kcat/Kmis the number to beat: it ranks substrates and caps at ~10⁸–10⁹ M⁻¹s⁻¹, the diffusion limit. An enzyme at that ceiling is "catalytically perfect" - it converts essentially every molecule it meets.
Current specificity constant
3.33 × 10⁶ M⁻¹s⁻¹ uninhibited
1.11 × 10⁶ M⁻¹s⁻¹ apparent
The Michaelis–Menten curve: velocity rises with substrate until every enzyme is busy, then plateaus at Vmax.
Image: fullofstars, Wikimedia Commons (CC BY-SA 3.0)