If chymotrypsin molecule undergoes a ser-195-ala mutation then –
Correct Answer: Chymotrypsin will bind the substrate but will not cause cleavage
Description: The substrate binds but does not cleave
Serine-195 is involved in catalytic activity but not in binding.
Serine-195 is the highly reactive residue of chymotrypsin.
The peptide bond is hydrolyzed through the acid-catalyzed nucleophilic attack, utilizing the serine 195 residue of the enzyme.
The enzyme-substrate complex is formed by the binding of the aromatic amino acid residue with the hydrophilic pocket on the active site of the enzyme (ser-195 has no role in binding).
Binding of substrate initiates proton shifts that in effect transfer the hydroxyl proton of ser 195 to Asp 102. This results in the formation of a covalent acyl-enzyme intermediate.
Further proton on Asp 102 then shuttles through His 57 to the amino group and the peptide bond is cleaved.
Thus, Asp 102-His 57-ser 195 constitute a "charge-relay network" that functions as a "proton shuttle".
Category:
Biochemistry
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