The following data describe the catalysis of cleavage of peptide bonds in small peptides by the enzyme elastase.
Substrate | KM (mM) | kcat(s−1) |
PAPA↓G | 4.0 | 26 |
PAPA↓A | 1.5 | 37 |
papa↓f | 0.64 | 18 |
The arrow indicates the peptide bond cleaved in each case.
(a) If a mixture of these three substrates was presented to elastase with the concentration of each peptide equal to 0.5 mM, which would be digested most rapidly? Which most slowly? (Assume enzyme is present in excess.)
(b) On the basis of these data, suggest what features of amino acid sequence dictate the specificity of proteolytic cleavage by elastase.
(c) Elastase is closely related to chymotrypsin. Suggest two kinds of amino acid residues you might expect to find in or near the active site.
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