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Question: A subtilisin with an active site mutation of His t...
EDIT QUESTION
A subtilisin with an active site mutation of His to Ala had a substantially decreased rate of reaction with the substrate Phe-Ala-Gln-Phe-X (cleavage site between Phe and X). Which of the following would have a reaction rate similar to native subtilisin?
A.
His-Ala-Gln-Phe-X
B.
Phe-His-Gln-Phe-X
C.
Phe-Ala-His-Phe-X
D.
Phe-Ala-Gln-His-X
E.
None of the answers is correct.
Would the answer for this one be D?
Yes, the answer would be D.
To determine the correct answer, we need to understand the impact of the active site mutation of His to Ala on the reaction rate and identify the suitable substitute for the native subtilisin.
The substrate for the subtilisin enzyme in question is Phe-Ala-Gln-Phe-X, where the cleavage site is between Phe and X. The mutation of His to Ala at the active site has substantially decreased the reaction rate.
In the wild-type or native subtilisin enzyme, the His residue at the active site is likely involved in the catalytic mechanism and is crucial for efficient substrate binding and cleavage. Thus, with the His residue mutated to Ala, it is necessary to find a substitution that can restore the catalytic activity.
Let's evaluate the options:
A. His-Ala-Gln-Phe-X: Since the original amino acid mutation was from His to Ala, this option does not restore the His residue at the active site. This substitution is unlikely to have a similar reaction rate as native subtilisin.
B. Phe-His-Gln-Phe-X: This substitution also does not restore the His residue at the active site. Hence, it is unlikely to have a similar reaction rate.
C. Phe-Ala-His-Phe-X: Here, the His residue is restored at the active site. This substitution has the potential to restore the reaction rate similar to native subtilisin.
D. Phe-Ala-Gln-His-X: In this case, the His residue is positioned after the cleavage site (between Phe and X). Therefore, it does not restore the His residue's function at the active site and is unlikely to have a similar reaction rate.
E. None of the answers is correct: This option must be considered if none of the substitutions mentioned in the previous options can restore the reaction rate similar to native subtilisin.
Based on the analysis, option C (Phe-Ala-His-Phe-X) is the most likely to have a reaction rate similar to the native subtilisin.