BIOC 3560 Lecture 8: Lecture 8
25 Sep 2018
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Document Summary
Enzyme regulation by proteolytic cleavage some enzymes are synthesized as an inactive precursor these enzymes are termed a zymogen if activated by a protease. Or: a proenzyme if activate by a non-protease zymogens are activated by the cleavage of specific peptide bonds this allows conformational changes in the enzyme to expose the active site. Note this form of activation is irreversible. Activation of chymotrypsin: many digestive system proteases are activated by proteolysis, many of these are serine proteases (ex. chymotrypsin) Ph sensitivity of chymotrypsin: his57 must be deprotonated like all serine proteases, the enzymatic activity of chymotrypsin is highly sensitive to ph. This allows his57 to act as a proton acceptor, inducing nucleophilic character in ser195 (critical to reaction mechanism) Alpha-amino group (newly formed as a result of proteolytic cleavage) of ile16 must be protonated. This allows ile16 to form an ion pair with asp194, stabilizing the active conformation of chymotrypsin. Formation of a blood clot is highly regulated.
