Question

Biochemistry The famous Anfinsen protein folding experiment was the first to show that the amino acid sequence of a protein can be sufficient to determine its structure. This experiment used the enzyme ribonuclease A, which contains four disulfide bonds. First, urea and beta-mercaptoethanol were added to a solution of RNase A, with the result that protein activity was lost. Next, urea was slowly removed by dialysis. Finally, beeta-mercaptoethanol was removed by dialysis, with the result that almost all of the original protein activity was regained. What happens when the order of the last two steps is swapped: beta-mercaptoethanol is removed first, then urea is removed.
A) Non-native disulfide bonds form after beta-mercaptoethanol is removed, so the protein cannot refold correctly
B) Half the original activity is regained
C) The original disulfide bonds reform, but the protein still cannot refold
D) The disulfide bonds do not reform, but activity is regained anyway
E) The protein still refolds the same way.

Answer 1

Answer:

The A option is the correct answer: Non-native disulfide bonds form after beta-mercaptoethanol is removed, so the protein cannot refold correctly

Explanation:

Beta-Mercaptoehanol is responsible to reduce the four disulfide bonds present in ARNase; Urea deals with non covalente bonds.  In presence of both ARNase is denatured.

If Urea is first removed by dialysis, and later is removed Beta-Mercaptoethanol, the enzyme recovers ist activity.

If Beta-Mercaptoethanol is first removed, disulfide bonds different from native use to be formed.  As a result ARNase is not an active enzyme