Enzyme Activity (Units) Calculator

Enzyme activity is defined as the amount of enzyme that converts 1 μmol of substrate per minute under specified conditions. One unit (U) equals 1 μmol substrate converted per minute. It's measured using spectrophotometric assays or by quantifying product formation over time.

Use the Beer-Lambert law: first convert ΔA/min to concentration change (mM/min) by dividing by extinction coefficient and path length. Then multiply by reaction volume and dilution factor to get μmol/min (enzyme units).

Specific activity is enzyme activity per unit mass of protein (U/mg). It indicates enzyme purity and efficiency. Higher specific activity means more active enzyme per milligram of protein, which is crucial for enzyme purification and quality assessment.

The dilution factor accounts for sample dilution before the assay. If you diluted your enzyme sample 1:10, use dilution factor = 10. If no dilution was made, use 1. This ensures accurate calculation of the original enzyme concentration.

Use spectrophotometric method when you can measure absorbance changes continuously (ΔA/min). Use product formation method when you measure the total amount of product formed over a specific time period. Both give equivalent results when properly calibrated.

Extinction coefficients vary by chromophore: NADH at 340nm = 6,220 M⁻¹·cm⁻¹, p-nitrophenol at 405nm = 18,500 M⁻¹·cm⁻¹. Always use the coefficient specific to your substrate/product and wavelength for accurate calculations.

Check your dilution factor, reaction volume units (should be mL), and extinction coefficient. Common errors include forgetting dilution corrections, using wrong volume units, or incorrect extinction coefficient values. Always perform a sanity check on results.