1. The following treatments or mutations of trypsin and chymotrypsin have at tim
ID: 282461 • Letter: 1
Question
1. The following treatments or mutations of trypsin and chymotrypsin have at times surprising outcomes. Explain the findings with each using your knowledge of the serine protease mechanism and catalysis. A. Mutation of Ser 195, His 57 or Asp 102 independently in the active site of chymotrypsin results in a 106-fold decrease in catalytic activity. Similarly, mutation of all three residues at the same time results in a 106-fold decrease in catalytic activity. B. Methyl-p-nitrobenzene sulfonate reacts with the catalytic His residue of chymotrypsin as shown in the figure below. After treatment with methyl-p-nitrobenzene sulfonate, the rate enhancement factor for chymotrypsin drops from 1010 to 2 x 106- fold. In part A, the rate enhancement factor of mutated chymotrypsin is around 5 x 104 - fold. In addition to explaining this finding, also explain why this treatment does not completely inhibit the enzyme as one might expect. His CH 0 0 Methyl-p-nitrobenzene sulfonate His 57 CH + 02N SO CH Unnumbered 15 p537 O Jehn Wley &Sons;, Inc.All rights reserved C. P-phenvlpropionate is a competitive inhibitor of chymotrypsin or of other proteases that have similar site-specificity. Propose whether or not you believe this molecule will reversibly react with the catalytic triad. CH2-CH2-COO B-PhenylpropionateExplanation / Answer
Ans 1. It means that all the three amino acids confer the activity to the chymotrypsin catalytic site and do not have a cumulative effect. This is why whether there is mutation in one acid at one time or all at same time, the catalytic activity
Ans 2. Because this reaction specifically add a methyl group to the histidine but do not majorly change it. Due to change in histidine at different site lead to less decrease in the catalytic activity compared to the case1.
Ans3. If it is a competitive inhibitor, then it will bind with the catalytic site of the chymotrypsin, and will affect the activity by same fold as in case of mutation, as the catalytic site is affected by either change in histidine or any other amino acid that lead to change in the active site.
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