Feedback for Multiple Choice Quiz 20

  1. To this list of general and specific enzyme stabilizing agents, we might also add b-mercaptoethanol to keep any Cys -SH groups reduced.

  2. Ammonium sulfate is the most-commonly used salt for gently precipitating proteins. AgCl is insoluble; the perchlorates are strong oxidizing agents; and guanidinium salts denature proteins.

  3. The protein elutes before the salt because it has much less of the column volume available to it.

  4. The four incorrect answers describe conditions under which the enzyme would not stick to the columns. With its pI of 5.1, BC-1ase would be negatively charged at pH 7 and would be expected to stick to the anion exchanger resin.

  5. In fact, all of these tests and possibly others should be applied to test for (in)homogeneity in the final preparation.

  6. AMP elution is the best idea. However, using high salt or changing the pH by +/- one unit might also work. Urea or distilled water are guaranteed to yield disappointing results.

  7. Follow the activity! Then determine the other characteristics of the prep to decide on the purity.

  8. Because the activity elutes after a protein with a known Mr = 25 kDa, the native Mr of BC-1ase must be larger than the 25 kDa given above. If the column were calibrated with other known proteins, we could get BC-1ase's Mr from the 35 mL elution volume.
  All of the correct answers have a green check mark.
  Incorrect answers have the "red-lit" button next to your choice.