Enzyme Activity Unit
One unit converts 1 µmol of substrate per minute.
Formula
Variables
How it works
Enzyme activity units tell you how fast an enzyme is working by measuring the amount of product formed, or substrate used up, per minute. One unit (U) is defined as the amount of enzyme that changes 1 micromole (µmol) of substrate each minute under specified conditions, so the formula converts a reaction rate into a standard lab measure. This works because enzyme reactions are time-dependent, and using micromoles per minute makes results comparable across experiments when temperature, pH, and substrate conditions are controlled.
When to use it
Use this when reporting or comparing enzyme assays in biochemistry, clinical chemistry, or lab practicals. It is especially useful when you need to convert a measured change in concentration over time into enzyme activity units.
Worked example, step by step
An enzyme assay produces 18 µmol of product in 6 minutes. U = \frac{\mu mol\ product}{min} U = \frac{18}{6} U = 3 Final answer: the enzyme activity is 3 U, meaning the enzyme converts 3 µmol of substrate per minute under these conditions.
Common mistakes to avoid
- Using millimoles or nanomoles without converting to micromoles first
- Forgetting that the time must be in minutes, not seconds or hours
- Assuming enzyme units measure enzyme mass instead of catalytic activity
Did You Know?
A single enzyme molecule can catalyse thousands to millions of reactions per second.
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