Understanding the Question Data

The correct answer is option (A): 50 fold purification was achieved with 25% yield of the enzyme.

Given purification table:

• Cell extract:
  • Volume = 8000 ml
  • Total protein = 400 mg
  • Total activity = 800 U
• DEAE Sephacel (ion-exchange step):
  • Volume = 10 ml
  • Total protein = 2 mg
  • Total activity = 200 U

From this data, the following quantities are calculated:

• Specific activity (SA) = Total activity / Total protein
• SA (cell extract) = 800 / 400 = 2 U/mg
• SA (DEAE Sephacel) = 200 / 2 = 100 U/mg
• Fold purification = SA (purified) / SA (crude) = 100 / 2 = 50 fold
• Percentage yield = (Final total activity / Initial total activity) × 100 = (200 / 800) × 100 = 25%

So the correct interpretation of the enzyme purification step is 50 fold purification with 25% yield, corresponding to option (A).

Why Option (A) Is Correct

Option (A) states: 50 fold purification was achieved with 25% yield of the enzyme.

• Fold purification:
  • Crude specific activity = 2 U/mg
  • Purified specific activity = 100 U/mg
  • Fold purification = 100 / 2 = 50 fold
• Yield:
  • Initial total activity = 800 U
  • Final total activity = 200 U
  • Percentage yield = (200 / 800) × 100 = 25%

Both the calculated fold purification and the percentage yield match the values in option (A), so this option is correct.

Why Option (B) Is Incorrect

Option (B) states: 25 fold purification was achieved with 50% yield of the enzyme.

• Fold purification:
  • A 25-fold purification would require purified specific activity = 25 × 2 = 50 U/mg.
  • The actual purified specific activity is 100 U/mg, which corresponds to a 50-fold purification, not 25-fold.
• Yield:
  • A 50% yield would require final activity = 0.5 × 800 = 400 U.
  • The actual final activity is 200 U, which corresponds to a 25% yield, not 50%.

Therefore, both the fold purification and the percentage yield given in option (B) are incorrect.

Why Option (C) Is Incorrect

Option (C) states: 50 fold purification was achieved with 4% yield of the enzyme.

• Fold purification:
  • The calculated fold purification is 50 (100 / 2 = 50 U/mg), so this part is correct.
• Yield:
  • A 4% yield would imply final activity = 0.04 × 800 = 32 U.
  • The actual final activity is 200 U, which corresponds to 25% yield, not 4%.

Thus, option (C) mixes a correct fold purification with an incorrect percentage yield.

Why Option (D) Is Incorrect

Option (D) states: 200 fold purification was achieved with 25% yield of the enzyme.

• Yield:
  • The percentage yield is correctly calculated as (200 / 800) × 100 = 25%.
• Fold purification:
  • A 200-fold purification would require purified specific activity = 200 × 2 = 400 U/mg.
  • The actual purified specific activity is 100 U/mg, corresponding to only a 50-fold purification.

Therefore, option (D) has a correct yield but an incorrect fold purification value.

Key SEO Takeaways for Exam Prep

• • Specific activity is a crucial parameter for assessing enzyme purification efficiency and is defined as enzyme units per mg of protein.

• • Fold purification is calculated as specific activity (purified) divided by specific activity (crude).

• • Percentage yield is calculated as (final total activity / initial total activity) × 100.

• • Such enzyme purification table problems are frequently asked in GATE and similar competitive exams, so accurate calculation of specific activity, fold purification, and yield is essential.