Enzyme Kinetics (Michaelis-Menten) Calculator Formula
Understand the math behind the enzyme kinetics (michaelis-menten) calculator. Each variable explained with a worked example.
Formulas Used
Reaction Velocity (v)
velocity = vmax * substrate / (km + substrate)v / Vmax
v_over_vmax = substrate / (km + substrate)Variables
| Variable | Description | Default |
|---|---|---|
vmax | Maximum Velocity (Vmax)(umol/min) | 100 |
km | Michaelis Constant (Km)(uM) | 50 |
substrate | Substrate Concentration [S](uM) | 25 |
How It Works
Michaelis-Menten Enzyme Kinetics
The Michaelis-Menten equation describes the rate of enzyme-catalyzed reactions as a function of substrate concentration.
Formula
v = Vmax × [S] / (Km + [S])
where Vmax is the maximum velocity, Km is the substrate concentration at half-Vmax, and [S] is the substrate concentration. When [S] = Km, v = Vmax/2. When [S] >> Km, v approaches Vmax.
Worked Example
An enzyme with Vmax = 100 umol/min and Km = 50 uM at [S] = 25 uM.
- 01v = 100 × 25 / (50 + 25)
- 02v = 2500 / 75 = 33.33 umol/min
- 03v/Vmax = 25/75 = 0.333 (33.3% of Vmax)
Frequently Asked Questions
What does Km represent biologically?
Km is the substrate concentration at which the enzyme operates at half its maximum rate. Low Km means high affinity (enzyme is efficient at low [S]). Typical Km values range from 0.1 uM to 10 mM.
When does the Michaelis-Menten model fail?
It fails for allosteric enzymes (sigmoidal kinetics), multi-substrate reactions, substrate inhibition, cooperative binding, and when the steady-state assumption does not hold.
How are Vmax and Km determined experimentally?
Measure initial velocities at several substrate concentrations. Plot v vs [S] for a direct fit, or use linearized plots (Lineweaver-Burk, Eadie-Hofstee, Hanes-Woolf) to extract the parameters.
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