Enzyme Activity Calculator
Calculate enzyme activity in units (µmol product per minute) and specific activity per milligram of protein from the product formed, reaction time and enzyme amount.
How it works
activity (U) = µmol product ÷ minutes · 1 U = 1 µmol/min = 1.667×10⁻⁸ kat · specific activity = activity ÷ mg protein
One enzyme unit (U) is defined as the amount of enzyme that converts one micromole of substrate into product per minute under defined conditions, so activity is simply the product formed divided by the reaction time. Dividing that activity by the milligrams of protein gives the specific activity — a measure of purity that rises as contaminating protein is removed during purification. The SI equivalent, the katal, is moles per second; one unit equals about 16.7 nanokatal.
Worked example
If a reaction produces 30 µmol of product in 10 minutes, the activity is 30 ÷ 10 = 3 U. With 0.5 mg of enzyme protein present, the specific activity is 3 ÷ 0.5 = 6 U/mg.
Sources: Enzyme unit — Wikipedia
Frequently asked questions
What is the difference between activity and specific activity?
Activity (units) is the total catalytic rate of your sample. Specific activity (units per mg protein) normalises that to the amount of protein, so it tracks enzyme purity — it climbs during purification as non-enzyme protein is removed.
What is a katal?
The SI unit of catalytic activity: one katal converts one mole of substrate per second. Because it is huge, biochemists usually report the older unit U (µmol/min); 1 U ≈ 16.7 nkat.
Do reaction conditions matter?
Very much. Activity is only comparable at the same temperature, pH and substrate concentration, which is why assay conditions are always specified alongside a unit definition.
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Educational estimate, not medical or laboratory advice — verify formulas, units and assumptions for your specific protocol.