The purification data for an enzyme is given below:
| Step | Process | Volume (ml) | Total protein (mg) | Total activity (Units) | Specific activity (Units/mg) |
|---|---|---|---|---|---|
| P | Cell-free extract | 17 | 177 | 102 | 0.58 |
| Q | Q-Sepharose | 14 | 18.8 | 72 | 3.83 |
| R | Phenyl Sepharose | 26 | 9.2 | 45 | 4.89 |
| S | Sephacryl S-200 | 7 | 4.1 | 30 | 7.32 |
Enzyme Purification Yield Calculation – Stepwise Explanation
The yield percentage during enzyme purification represents the amount of enzyme activity
retained after each purification step relative to the initial crude extract.
This problem is commonly asked in biochemistry competitive examinations.
Given Enzyme Purification Data
| Step | Process | Volume (ml) | Total Protein (mg) | Total Activity (Units) | Specific Activity (Units/mg) |
|---|---|---|---|---|---|
| P | Cell-free extract | 17 | 177 | 102 | 0.58 |
| Q | Q-Sepharose | 14 | 18.8 | 72 | 3.83 |
| R | Phenyl Sepharose | 26 | 9.2 | 45 | 4.89 |
| S | Sephacryl S-200 | 7 | 4.1 | 30 | 7.32 |
Formula Used
Yield (%) =
(Total activity at a given step / Total activity of initial extract) × 100
Initial total activity (Step P) = 102 Units
Step-by-Step Yield Calculation
Step P (Cell-free extract)
(102 / 102) × 100 = 100%
Step Q (Q-Sepharose)
(72 / 102) × 100 ≈ 71%
Step R (Phenyl Sepharose)
(45 / 102) × 100 ≈ 44%
Step S (Sephacryl S-200)
(30 / 102) × 100 ≈ 29%
Calculated Yield (%)
- P: 100%
- Q: 71%
- R: 44%
- S: 29%
Correct Answer
Option (D): P-100, Q-71, R-44, S-29
Explanation of Other Options
Option (A)
The values are approximately ten times lower than correct yields,
indicating incorrect scaling or decimal error.
Option (B)
These values do not use the initial activity as a reference and
therefore do not represent true yield percentages.
Option (C)
The percentages are incorrectly calculated by treating activity
values as fractions instead of percentages.
Key Takeaway
Yield percentage always decreases with successive purification steps
and must be calculated relative to the initial crude extract activity.
Hence, option (D) is the correct answer.
