Enzyme specificity and catalytic efficiency: Catalysis of the cleavage of peptid
ID: 1065971 • Letter: E
Question
Enzyme specificity and catalytic efficiency: Catalysis of the cleavage of peptide bonds in small peptides by a proteolytic enzyme (digests proteins) is described in the following table. Examine the table contents and using calculations answer the following two questions. The arrows indicate where the peptide bond is cleaved. If a mixture of these three peptides were added to the enzyme with the concentration of each peptide being the same, which peptide would be digested most rapidly and efficiently? Briefly explain your reasoning. The experiment was performed again on another peptide with following results. On the basis of the following data, suggest the features of the amino acid sequence that dictate the specificity of the enzyme.Explanation / Answer
a) The enzyme efficiency or the specificity constant of an enzyme to convert substrates into products is equal to kcat/KM. On the basis of comparison of specificity constants we can measure the preference of which enzyme will work more efficiently.
Therefore, from the given values in the table, Glu-Met-Thr-AlaPhe with maximum specificity constant (kcat/KM = 36) will digest the enzyme more efficiently.
b) The specificity constant is reduced significantly on replacing Ala with Ile in Glu-Met-Thr-IlePhe. Here, (kcat/KM = 2). This suggests steric limitations on replacing Ala with Ile i.e., when a simple methyl group in Ala is replaced with a branched bulkier hydrocarbon in Ile at the binding site, the specificity is hindered dramatically.
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