What you are given
- Activity (U/mL): 50
- Volume (mL): 2
- Protein (mg/mL): 5
Formula: specific activity = U / mg
Protein
How do you calculate enzyme activity?
Total units and specific activity from a measured rate. The relationship used is specific activity = U / mg.
Worked example
Every number below is computed by the calculator, not typed in
The working
- Total units:
unitsPerMl · volumeMl = 50 U/mL · 2 mL=100 U - Total protein:
proteinMgPerMl · volumeMl = 5 mg/mL · 2 mL=10 mg - Specific activity:
totalUnits / totalProteinMg = 100 U / 10 mg=10 U/mg
Specific activity is 10 U/mg.
What each symbol means
- aₛₚ: Specific activity (U/mg)
- CU: Activity concentration (U/mL)
- CP: Protein concentration (mg/mL)
- V: Sample volume (mL)
A printable one-page version is on the formula sheet.
Try it yourself
Two problems, with the working revealed
Problem 1 Enzyme activity
Work out the result for enzyme activity.
- Activity (U/mL): 10
- Volume (mL): 2
- Protein (mg/mL): 5
Show the answer and the working
Specific activity is 2 U/mg.
- Total units:
unitsPerMl · volumeMl = 10 U/mL · 2 mL=20 U - Total protein:
proteinMgPerMl · volumeMl = 5 mg/mL · 2 mL=10 mg - Specific activity:
totalUnits / totalProteinMg = 20 U / 10 mg=2 U/mg
Open this in the calculator to change the numbers.
Problem 2 Enzyme activity
Work out the result for enzyme activity.
- Activity (U/mL): 50
- Volume (mL): 2.5
- Protein (mg/mL): 5.5
Show the answer and the working
Specific activity is 9.091 U/mg.
- Total units:
unitsPerMl · volumeMl = 50 U/mL · 2.5 mL=125 U - Total protein:
proteinMgPerMl · volumeMl = 5.5 mg/mL · 2.5 mL=13.75 mg - Specific activity:
totalUnits / totalProteinMg = 125 U / 13.75 mg=9.091 U/mg
Open this in the calculator to change the numbers.
Do it with your own numbers.
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