1. What is Enzyme Activity?

Enzyme activity is a measure of the catalytic ability of an enzyme, typically expressed as micromoles of substrate converted per minute per milligram of enzyme (U/mg). It's calculated from absorbance changes in spectrophotometric assays.

2. How Does the Calculator Work?

The calculator uses the enzyme activity equation:

Where:

• \( A \) — Absorbance (dimensionless)
• \( \epsilon \) — Molar extinction coefficient (L/mol·cm)
• \( l \) — Path length (cm)
• \( time \) — Reaction time (minutes)
• \( [E] \) — Enzyme concentration (mg/mL)

Explanation: The equation converts absorbance measurements into enzyme activity units by accounting for the assay conditions and enzyme concentration.

3. Importance of Enzyme Activity Measurement

Details: Measuring enzyme activity is crucial for enzyme characterization, purification monitoring, and determining specific activity for quality control in enzyme production.

4. Using the Calculator

Tips: Enter absorbance value, molar extinction coefficient for your substrate, path length (typically 1 cm for standard cuvettes), reaction time, and enzyme concentration. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical units for enzyme activity?
A: Activity is typically expressed in Units/mg, where 1 Unit = 1 μmol substrate converted per minute.

Q2: How do I determine the extinction coefficient?
A: The extinction coefficient is substrate-specific and can be found in literature or determined experimentally.

Q3: What if my path length isn't 1 cm?
A: Adjust the path length value in the calculator. Many spectrophotometers use 1 cm path length cuvettes by default.

Q4: Should I use initial rate measurements?
A: Yes, enzyme activity calculations are most accurate when using initial linear rates before substrate depletion occurs.

Q5: How does temperature affect the calculation?
A: Enzyme activity is temperature-dependent. Always report the temperature at which the assay was performed.