MCAT Biochemistry Question 44: Answer and Explanation

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Question: 44

14. A protein collected through affinity chromatography displays no activity even though it is found to have a high concentration using the Bradford protein assay. What best explains these findings?

  • A. The Bradford reagent was prepared incorrectly.
  • B. The active site is occupied by free ligand.
  • C. The protein is bound to the column.
  • D. The protein does not catalyze the reaction of interest.

Correct Answer: B

Explanation:

Protein activity and concentration are generally correlated. Because we have a high concentration of protein, we expect a high activity unless the protein has been damaged or inactivated in some way. The protein could have been inactivated by experimental conditions like detergents, heat, or pH; however, these are not answer choices. Rather, we must consider how the experimental procedure works. Protein elutes off of an affinity column by binding free ligand. In this situation, the binding may not have been reversed and thus the free ligand competes for the active site of the enzyme, lowering its activity.

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