Enter Enzyme Details
Use values from the same activity assay. The dilution factor estimates concentration in the original stock.
Important Assumption
This calculator estimates molecular concentration from catalytic activity. Use matching assay conditions for activity and specific activity. For high-stakes laboratory decisions, verify results with an independent concentration method.
Formula Used
The calculator first corrects measured activity for dilution. It then converts activity into protein mass. Finally, it divides mass concentration by molecular weight.
Molarity (mol/L) = [Activity (U/mL) × Dilution Factor ÷ Specific Activity (U/mg) × Purity Fraction] ÷ Molecular Weight (g/mol)
Because 1 mg/mL equals 1 g/L numerically, the final division produces mol/L. Purity fraction equals purity percent divided by 100.
How to Use This Calculator
1. Enter the measured activity
Type the enzyme activity concentration from your assay. Choose the matching activity unit.
2. Add specific activity
Enter the activity per milligram, microgram, or gram of protein. Use a value generated by a compatible assay.
3. Enter molecular weight
Use the mass of the active molecular form. Select Da or kDa as needed.
4. Apply corrections
Enter the total dilution factor and target-protein purity. Add sample volume to calculate total quantities.
5. Review all concentration scales
Select Calculate Molarity. Review molar, millimolar, micromolar, and nanomolar outputs before using the result.
Example Data
This example shows a simple undiluted preparation. It assumes a purified enzyme.
| Input | Example value | Purpose |
|---|---|---|
| Activity | 100 U/mL | Measured enzyme activity |
| Specific activity | 500 U/mg | Protein mass conversion |
| Molecular weight | 50,000 g/mol | Mass-to-mole conversion |
| Dilution factor | 1 | No dilution correction |
| Purity | 100% | No purity adjustment |
| Estimated result | 4.0 × 10-6 M | 4.0 µM |
Understanding U/mL and Molarity
Enzyme activity and molarity answer different laboratory questions. U/mL describes reaction capacity in a liquid. Molarity describes molecules within a volume. A conversion needs supporting protein data. Specific activity links activity to protein mass. Molecular weight links protein mass to molecular amount. This calculator combines values in one workflow. It helps with preparation, assay planning, and dilution design. Results remain estimates when purity, recovery, or assay conditions are uncertain. Always compare calculated values with your laboratory records before preparing reactions.
Why Specific Activity Matters
A unit measures reaction rate. Its meaning depends on the assay. One unit may represent one micromole product per minute. Assay conditions can alter activity. Temperature, pH, substrate level, and cofactors matter. Specific activity reports units per milligram of protein. Divide U/mL by U/mg. The result is milligrams of protein per millilitre. This step converts functional activity into mass concentration. Use a value measured under similar conditions. Supplier documents list a typical specific activity. Check that figure before preparing formulations.
Using Molecular Weight Correctly
Molecular weight changes protein mass into moles. Enter monomeric mass when one molecule performs the activity. Enter complex mass when the active assembly is needed. Supplier documents often report mass in daltons or kilodaltons. One dalton equals one g/mol numerically. A 50 kDa enzyme has a molecular weight of 50,000 g/mol. The calculator accepts both formats. Check whether tags, glycosylation, or subunits change the mass. These details can shift the result. Use the molecular form that matches your experiment.
Dilution and Purity Adjustments
Diluted assay results do not equal stock concentration. Multiply measured activity by the dilution factor. A tenfold dilution needs a factor of ten. Include serial dilution steps. The calculator then estimates original enzyme concentration. Purity provides a separate target-protein adjustment. A 90 percent setting counts ninety percent of protein mass. Leave purity at 100 percent when specific activity represents purified enzyme. Do not apply purity twice. Keep a record of every assumption. This supports later comparisons and safer laboratory decisions.
Practical Laboratory Checks
Use one activity definition for both values. Do not combine units from incompatible assays. Confirm U/mL and specific activity share assay conditions. Enter positive numbers only. Low concentrations read easily in micromolar or nanomolar units. The results show scales for this reason. Sample volume is optional. When supplied, it estimates protein mass, enzyme amount, and total activity. Totals help with aliquoting and reaction setup. Round working concentrations sensibly. Keep more digits during planning. Repeat calculations after changing dilution or purity.
Limits of the Conversion
This conversion cannot directly measure molecular concentration. It infers concentration from catalytic activity. Inactive enzyme, inhibitors, denaturation, and interference can lower activity. Different isoforms can have different specific activities. Treat results as careful planning estimates. Use absorbance, mass spectrometry, or protein assays when exact concentration matters. Regulated work needs documented assay methods and reference material. Compare calculated values with batch records. Investigate major differences before using samples in sensitive experiments. Good inputs produce useful, defensible calculations for daily laboratory work.
Frequently Asked Questions
1. Can U/mL convert directly to molarity?
No. You need specific activity and molecular weight. U/mL measures catalytic activity. Molarity measures molecular amount. Specific activity bridges activity and protein mass. Molecular weight bridges mass and moles.
2. What is specific activity?
Specific activity is enzyme activity per amount of protein. It is often listed as U/mg. Higher specific activity usually indicates a more active or more purified enzyme preparation.
3. Why is molecular weight required?
Molecular weight converts protein mass into moles. Without it, the calculator can estimate mg/mL but cannot calculate molarity.
4. Should I use Da or kDa?
Use either format. One kDa equals 1,000 Da. Select the matching unit before calculating. The calculator converts both choices to g/mol internally.
5. What does the dilution factor do?
It estimates concentration in the original stock. Use 1 when no dilution occurred. Use 10 after a tenfold dilution. Multiply all serial dilution factors together.
6. When should purity be less than 100%?
Use a lower value when only part of the measured protein mass is the target enzyme. Keep it at 100% when your specific activity already represents purified target enzyme.
7. Can I use total sample volume?
Yes. Volume is optional. It provides estimated total protein mass, total enzyme moles, and total activity in the sample.
8. Why are my values shown in several concentration units?
Enzyme concentrations are often very small. M, mM, µM, and nM views make results easier to compare with protocols, assay requirements, and reaction volumes.
9. Does one enzyme unit always mean one micromole per minute?
Not always. Many assays use that definition, but unit definitions vary. Follow the supplier or assay protocol. Use compatible activity and specific activity values.
10. Can inactive enzyme affect the result?
Yes. Low activity from inactivation, inhibitors, or assay conditions can lower the calculated estimate. Use a suitable independent method when exact molecular concentration is important.
11. Is this result suitable for regulated work?
It is useful for planning. Regulated work may require validated assays, traceable standards, documented calculations, and independent concentration confirmation.