How is specific activity calculated?

Specific activity is total enzyme units divided by total protein in milligrams, giving units per milligram. It measures purity: as contaminating proteins are removed, the same activity is carried by less protein, so specific activity rises.

What does purification fold mean?

Purification fold is the specific activity of a step divided by the specific activity of the starting crude extract. A 10-fold value means the enzyme is ten times purer than where you began, regardless of how much total activity was lost.

How is percent yield defined?

Percent yield is the total units recovered in a step divided by the total units in the crude extract, times 100. It tracks how much of your active enzyme survived purification. Yield falls at every step while fold should rise.

What units should I enter?

Volume in millilitres, protein concentration in milligrams per millilitre, and activity in units per millilitre. As long as you stay consistent the table is correct. Total protein is volume times concentration and total units is volume times activity.

Why does my fold rise while yield falls?

That is the normal and desired pattern. Each step discards contaminating protein, so purity (fold) climbs, but some target enzyme is inevitably lost too, so recovery (yield) drops. A good purification maximises fold while keeping yield acceptable.

Protein Yield & Recovery Calculator

A protein purification table is the scorecard of any enzyme isolation. It records, step by step, how much total protein and how much catalytic activity you carry forward, and from those two numbers it derives the metrics that tell you whether the purification is working: specific activity, yield, and fold purification.

How it works

For each fraction you provide three measured quantities, and the table computes the rest:

total protein (mg) = volume (mL) x protein conc (mg/mL)
total units        = volume (mL) x activity (U/mL)
specific activity  = total units / total protein      (U/mg)
yield %            = (step total units / crude total units) x 100
fold purification  = step specific activity / crude specific activity

The first row you enter is treated as the crude starting material and becomes the 100 percent yield, 1.0-fold reference for everything below it.

Example and notes

Imagine a crude extract of 100 mL at 10 mg/mL carrying 5 U/mL. That is 1000 mg of protein and 500 units, for a specific activity of 0.5 U/mg. After an ammonium sulphate cut you might have 20 mL at 8 mg/mL and 20 U/mL: 160 mg, 400 units, specific activity 2.5 U/mg. The yield is 80 percent and the fold is 5. Activity is mostly retained while purity has climbed fivefold, exactly the trade-off you want. Rows with zero protein are skipped for specific activity to avoid dividing by zero.