Question 8

(a) Name the three essential active site residues of chymotrypsin and describe how each is involved in the catalytic mechanism.

(b) Describe the substrate specificity of chymotrypsin and the structural feature that determines this specificity.

(c) Briefly describe the following methods of regulation of enzyme activity in a cell

i) allosteric control

ii) covalent modification

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Jarrod RobelLv2

17 Oct 2018

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Using site specific mutagenesis to change residues in the substrate binding cleft of PKA (not residues involved in catalytic roles), how would you alter PKAâs substrate specifity? By this, I mean how would you specifically make mutations in the PKA enzyme amino acid sequence (not the substrate sequence) that would alter amino acid preferences for particular residues on a substrate peptide that you might want to design for this enzyme. Please think carefully about what this means. It does not mean changing ATP binding or altering the active site base or Mg binding site, as such mutations would only decrease overall catalytic activity of the phosphotransfer reaction. Please provide three detailed examples of how you could try to modify the substrate specificity of PKA (assuming that protein sequences exist in the cell that would match the newly designed substrate specificity of the enzyme).

Explain how the following mechanisms regulate enzyme activity.

Part A

Covalent modification

a)The product of a series of reactions acts as an inhibitor for an earlier reaction.

b)Hormones control the synthesis of enzymes.

c)A regulator binds to the enzyme at a site other than the active site. This binding changes the shape of the enzyme and alters the catalytic ability of the enzyme.

d)An inhibitor binds reversibly to the enzymesubstrate complex, blocking the binding of the second substrate to the active site.

e)The activity of an enzyme is influenced by the addition or removal of a group that is covalently bonded to the enzyme.

f)An inhibitor forms covalent bonds to the active site, permanently blocking it.

Part B

Genetic control

a)The product of a series of reactions acts as an inhibitor for an earlier reaction.