4. The protein concentration and enzyme activity in 100 mL of a cell free extract is 5 mg/mL and 2 units/mL,
respectively. After multiple steps of purification, the final 10 mL fraction contains 4 mg/mL of protein and 15
units/mL of enzyme activity. The fold purification and percentage recovery, respectively is:
1. 10 and 75
2. 9.4 and 20
3. 9.4 and 75
4. 10 and 20

Title:
How to Calculate Fold Purification and Percentage Recovery in Enzyme Purification

How to Calculate Fold Purification and Percentage Recovery in Enzyme Purification

Enzyme purification involves separating a target enzyme from other proteins or cellular material. Two key metrics to evaluate the success of purification steps are:

• Fold Purification: How much purer the enzyme becomes.

• Percentage Recovery: How much of the original enzyme activity is retained.

Let’s work through a common example.

Question:

The protein concentration and enzyme activity in 100 mL of a cell-free extract are 5 mg/mL and 2 units/mL, respectively. After purification, the final 10 mL fraction contains 4 mg/mL of protein and 15 units/mL of enzyme activity.

What are the fold purification and percentage recovery, respectively?

Options:

1. 10 and 75

2. 9.4 and 20

3. 9.4 and 75

4. 10 and 20

Step-by-Step Calculation

1. Calculate Total Activity (Before and After Purification)

Initial total activity =

$$100\text{mL}\times 2\text{units/mL}=200\text{units}$$

Final total activity =

$$10\text{mL}\times 15\text{units/mL}=150\text{units}$$

2. Calculate Total Protein (Before and After Purification)

Initial total protein =

$$100\text{mL}\times 5\text{mg/mL}=500\text{mg}$$

Final total protein =

$$10\text{mL}\times 4\text{mg/mL}=40\text{mg}$$

3. Calculate Specific Activity (Activity per mg protein)

Initial specific activity =

200 units500 mg=0.4 units/mg\frac{200\ \text{units}}{500\ \text{mg}} = 0.4\ \text{units/mg}500 mg200 units​=0.4 units/mg

Final specific activity =

150 units40 mg=3.75 units/mg\frac{150\ \text{units}}{40\ \text{mg}} = 3.75\ \text{units/mg}40 mg150 units​=3.75 units/mg

4. Fold Purification

Fold Purification=3.750.4=9.375≈9.4\text{Fold Purification} = \frac{3.75}{0.4} = 9.375 \approx 9.4Fold Purification=0.43.75​=9.375≈9.4

5. Percentage Recovery

Recovery %=(150200)×100=75%\text{Recovery \%} = \left(\frac{150}{200}\right) \times 100 = 75\%Recovery %=(200150​)×100=75%

✅ Correct Answer: (3) 9.4 and 75

Why This Matters

Understanding fold purification and percentage recovery helps biochemists:

• Assess the efficiency of each purification step

• Balance purity vs. yield for industrial and research applications

• Optimize purification protocols for cost and performance

Summary

• Fold purification shows the increase in enzyme purity: 9.4x

• Percentage recovery indicates how much enzyme activity remains: 75%

Answer: Option (3) — 9.4 and 75