Specific Activity Calculator (U/mg protein)

Specific Activity Calculator (U/mg protein) | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Education
Input types: select, number
Output type: json
Sample coverage: 4
API ready: Yes

Overview

The Specific Activity Calculator finds enzyme activity per milligram of protein using total activity and protein mass, or activity and protein concentrations. It reports the result in U/mg and converts it to nkat/mg for purification records and educational laboratory planning.

When to use

Compare enzyme enrichment across purification fractions.
Calculate specific activity directly from U and mg protein measurements.
Convert a U/mg result to nkat/mg for SI-based reporting.

How it works

1Choose total activity plus protein mass, or activity concentration plus protein concentration.
2Enter the matching activity and protein values from the same sample.
3The calculator divides activity by protein amount; in concentration mode it divides U/mL by mg/mL.
4The result is rounded to the selected number of decimal places and shown in U/mg and nkat/mg.

Use cases

Fill purification tables with specific activity for each fraction.
Compare enzyme enrichment after chromatography or other purification steps.
Summarize routine activity-assay and protein-assay results in U/mg and nkat/mg.

Examples

1. Purification fraction: 40 U in 5 mg protein

Protein purification student

Background

A purification fraction contains 40 U of enzyme activity and 5 mg of total protein.

Problem

The specific activity is needed for a purification table and comparison with other fractions.

How to use

Select total activity plus protein mass, enter 40 U and 5 mg, and set decimal places to 2.

Mode: Total activity + protein mass; Enzyme Activity: 40 U; Protein Mass: 5 mg; Decimal Places: 2

Outcome

The result is 8 U/mg, equivalent to 133.33 nkat/mg.

2. QC sample: 250 U/mL over 10 mg/mL

Biochemistry laboratory analyst

Background

A stock sample measures 250 U/mL in the activity assay and 10 mg/mL in the protein assay.

Problem

The analyst wants the specific activity without calculating total sample volume.

How to use

Select activity plus protein concentration, enter 250 U/mL and 10 mg/mL, and set decimal places to 2.

FAQ

What is specific activity?

Specific activity is enzyme activity per milligram of total protein, expressed as U/mg.

Which calculation modes are available?

You can use total activity and protein mass, or activity concentration and protein concentration.

Do I need to enter a sample volume?

No. In concentration mode, divide U/mL by mg/mL directly; the volume units cancel.

How is U/mg converted to nkat/mg?

The calculator uses 1 U = 16.67 nkat, so it multiplies U/mg by 16.67.

Can this calculator determine enzyme purity?

It calculates specific activity, a commonly used purity metric. It does not independently measure purity or replace experimental assays.

Mode: Activity + protein concentration; Activity Concentration: 250 U/mL; Protein Concentration: 10 mg/mL; Decimal Places: 2

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Purification fraction: 40 U in 5 mg protein

2. QC sample: 250 U/mL over 10 mg/mL

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