Enzyme Calculator
Enzyme Activity Calculator
A comprehensive tool for calculating enzyme activity, kinetics, and inhibition effects
Activity Calculation
Calculate enzyme activity based on absorbance, concentration, and time
Kinetics Analysis
Plot Michaelis-Menten curves and determine Km and Vmax
Inhibition Studies
Analyze competitive, non-competitive, and uncompetitive inhibition
How to Use This Calculator
- Select the calculation type from the left menu
- Enter your experimental parameters
- Adjust temperature and pH if needed
- Click "Calculate" to see results
- View graphical representations of your data
- Use the unit converter for different measurements
Enzyme Kinetics
Michaelis-Menten Parameters
Lineweaver-Burk Plot
Kinetics Theory
Michaelis-Menten Equation
Where:
- V₀ is the initial reaction rate
- Vmax is the maximum reaction rate
- [S] is the substrate concentration
- Km is the Michaelis constant (substrate concentration at half Vmax)
Lineweaver-Burk Equation
The Lineweaver-Burk plot is a double reciprocal plot that linearizes the Michaelis-Menten equation, making it easier to determine Km and Vmax.
Enzyme Inhibition Analysis
Inhibition Parameters
Inhibition Effects
Inhibition Theory
Types of Enzyme Inhibition
Competitive Inhibition
Inhibitor competes with substrate for active site. Increases apparent Km, no effect on Vmax.
Non-competitive
Inhibitor binds elsewhere, reducing enzyme efficiency. Decreases Vmax, no effect on Km.
Uncompetitive
Inhibitor binds only to enzyme-substrate complex. Decreases both Km and Vmax.
Unit Converter
Enzyme Activity Units
Unit Definitions
| Unit | Definition | Conversion |
|---|---|---|
| U (Unit) | Amount of enzyme that catalyzes 1 μmol of substrate per minute | 1 U = 1 μmol/min |
| kat (katal) | Amount of enzyme that catalyzes 1 mol of substrate per second | 1 kat = 6 × 10⁷ U |
| U/mL | Units per milliliter (activity concentration) | - |
| U/mg | Units per milligram (specific activity) | - |
Help & Tutorial
Getting Started
Basic Enzyme Activity Calculation
- Navigate to the "Activity Calculator" section
- Enter your substrate concentration in mol/L
- Enter your enzyme concentration in mg/mL
- Input the reaction time in minutes
- Enter the change in absorbance (ΔA)
- Provide the molar absorptivity (ε) - default is for NADH at 340 nm
- Enter the path length (usually 1 cm)
- Click "Calculate Activity" to see results
Understanding the Results
- Activity (U/mL): Enzyme activity per milliliter of solution
- Specific Activity (U/mg): Activity per milligram of enzyme protein
- Reaction Rate (μmol/min): Amount of substrate converted per minute
- Turnover Number (min⁻¹): Number of substrate molecules converted per enzyme molecule per minute
Advanced Features
Enzyme Kinetics Analysis
In the "Enzyme Kinetics" section, you can:
- Plot Michaelis-Menten curves by entering Vmax and Km values
- Generate Lineweaver-Burk plots for linearized analysis
- View theoretical explanations of enzyme kinetics
Inhibition Studies
In the "Inhibition Analysis" section, you can:
- Simulate different types of enzyme inhibition (competitive, non-competitive, uncompetitive)
- Adjust inhibitor concentration and Ki values
- Visualize how inhibition affects enzyme kinetics
Unit Conversion
The "Unit Converter" allows you to convert between common enzyme activity units:
- U/mL (Units per milliliter)
- μmol/min (micromoles per minute)
- nmol/min (nanomoles per minute)
- kat (katal)
- U/mg (Units per milligram)
Frequently Asked Questions
The standard unit of enzyme activity is the Unit (U), defined as the amount of enzyme that catalyzes the conversion of 1 micromole of substrate per minute under specified conditions. In the SI system, the katal (kat) is used, which represents the conversion of 1 mole of substrate per second (1 kat = 6 × 10⁷ U).
The molar absorptivity (ε) is a property of your substrate or product that absorbs light. For common assays:
- NADH at 340 nm: ε = 6.22 mM⁻¹cm⁻¹ (6220 M⁻¹cm⁻¹)
- p-Nitrophenol at 405 nm: ε ≈ 18.5 mM⁻¹cm⁻¹
- Check literature for your specific compound or perform a standard curve with known concentrations
Activity (U/mL) measures the total enzyme activity per volume of solution, while Specific Activity (U/mg) measures the activity per milligram of enzyme protein. Specific activity is a measure of enzyme purity - it increases as the enzyme is purified from other proteins.
Enzyme Activity Theory
Enzyme Activity Fundamentals
What is Enzyme Activity?
Enzyme activity refers to the catalytic ability of an enzyme to convert substrate to product. It is typically measured as the amount of substrate converted (or product formed) per unit time under defined conditions.
Standard Activity Calculation
The most common method for determining enzyme activity spectrophotometrically uses the Beer-Lambert law:
Where:
- ΔA/min = Change in absorbance per minute
- ε = Molar absorptivity (M⁻¹cm⁻¹)
- L = Path length (cm)
Factors Affecting Enzyme Activity
Temperature
Enzyme activity typically increases with temperature up to an optimum, then decreases due to denaturation. The Q₁₀ rule states that activity roughly doubles for every 10°C increase (up to the optimum).
pH
Each enzyme has an optimal pH where activity is maximal. Changes in pH can affect enzyme structure and the ionization states of active site residues.
Substrate Concentration
Activity increases with substrate concentration until all active sites are saturated (Vmax). This relationship is described by the Michaelis-Menten equation.
Inhibitors
Molecules that reduce enzyme activity. Can be competitive (compete with substrate), non-competitive (bind elsewhere), or uncompetitive (bind only to ES complex).
Enzyme Kinetics
Michaelis-Menten Kinetics
Most enzymes follow Michaelis-Menten kinetics, characterized by:
- Vmax: Maximum velocity achieved at saturating substrate concentrations
- Km: Michaelis constant - substrate concentration at half Vmax. Represents enzyme-substrate affinity
- kcat: Turnover number - number of substrate molecules converted per enzyme molecule per second
Key Equations
Michaelis-Menten Equation
Turnover Number (kcat)
Catalytic Efficiency
Specific Activity
Practical Considerations
Assay Conditions
For accurate activity measurements:
- Use initial rates (first 5-10% of reaction)
- Ensure substrate is not limiting (≥10× Km for Vmax measurements)
- Maintain constant temperature (±0.1°C)
- Use appropriate buffer with adequate capacity
- Include necessary cofactors
Common Pitfalls
Substrate Depletion
Measuring beyond initial rates leads to underestimation of activity as substrate is consumed and product accumulates.
Enzyme Instability
Enzyme may denature during assay. Use short incubation times and stabilize conditions.
Improper Blanking
Failure to properly blank the spectrophotometer with reaction mixture (minus enzyme or minus substrate).
Non-linear Range
Absorbance readings outside the instrument's linear range (typically 0.1-1.0 AU) lead to inaccurate measurements.
Quick Reference
Standard Units:
- 1 U = 1 μmol/min
- 1 kat = 6 × 10⁷ U
Common ε Values:
- NADH (340 nm): 6.22 mM⁻¹cm⁻¹
- pNP (405 nm): 18.5 mM⁻¹cm⁻¹
Recent Calculations
No recent calculations
Temperature Effects
Typical enzyme temperature activity profile showing optimal temperature range.
Designed for Biochemistry Education