Substrate Calculator
Calculate reaction velocity, substrate conversion and catalytic efficiency using the Michaelis-Menten equation. Perfect for biochemistry, enzymology and metabolic studies.
How the substrate calculator works
This calculator uses the Michaelis-Menten equation to determine the reaction rate (velocity) of an enzyme-catalysed reaction. Enter the Vmax (maximum reaction rate), Km (Michaelis constant) and substrate concentration [S] to get the reaction velocity, substrate conversion percentage, catalytic efficiency and more.
The Michaelis-Menten equation is: v = (Vmax × [S]) / (Km + [S]). It describes how reaction rate depends on substrate concentration — at low [S], the rate is proportional to [S]; at high [S], the rate approaches Vmax.
Step 1: Enzyme Parameters
Understanding Vmax and Km
Vmax is the maximum reaction rate when the enzyme is fully saturated with substrate. Km is the substrate concentration at which the reaction rate is half of Vmax — lower Km means higher substrate affinity.
Step 2: Substrate Conditions
Michaelis-Menten Kinetics
The reaction velocity v = (Vmax × [S]) / (Km + [S]). At low [S], the reaction is first-order; at high [S], it approaches zero-order (Vmax). The ratio kcat/Km measures catalytic efficiency.
Substrate Kinetics Results
Reaction Velocity (v)
Substrate Concentration Comparison
| [S] (mM) | Reaction Velocity (μmol/min) | % of Vmax | Order |
|---|
Michaelis-Menten Plot
Michaelis-Menten Equation
v = (Vmax × [S]) / (Km + [S])
v = reaction velocity · Vmax = maximum reaction rate · [S] = substrate concentration · Km = Michaelis constant (substrate concentration at ½ Vmax)
Frequently Asked Questions
What is the Michaelis-Menten equation?
The Michaelis-Menten equation describes the rate of enzymatic reactions: v = (Vmax × [S]) / (Km + [S]), where v is the reaction velocity, Vmax is the maximum reaction rate, [S] is the substrate concentration, and Km is the Michaelis constant.
What does Km mean in enzyme kinetics?
Km (Michaelis constant) is the substrate concentration at which the reaction rate is half of Vmax. It reflects the affinity of the enzyme for its substrate — a lower Km means higher affinity.
What is catalytic efficiency?
Catalytic efficiency is the ratio kcat / Km, where kcat is the turnover number (molecules of substrate converted per enzyme molecule per second). It measures how efficiently an enzyme converts substrate to product.
How do you calculate reaction rate from Vmax and Km?
Using the Michaelis-Menten equation: v = (Vmax × [S]) / (Km + [S]). Simply plug in your Vmax, Km and substrate concentration values to get the reaction velocity.
What is the difference between Vmax and kcat?
Vmax is the maximum reaction rate when all enzyme active sites are saturated with substrate. kcat (turnover number) is Vmax divided by the total enzyme concentration, representing the number of substrate molecules converted per enzyme molecule per second.
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