Dorka Beri, Asst. Prof. In Biochemistry, GCW (A), Guntur
Zymogen Activation
A zymogen is like a wrapped candy bar. In order to get to the good stuff, you need to tear away what's keeping you from it. Zymogens, or proenzymes, are enzymes that aren't functioning yet because their action is blocked by a 'wrapper'. The 'wrapper' can be a link between two amino acids other enzymes are synthesized as inactive precursors that are subsequently activated by cleavage of one or a few specific peptide bonds. The inactive precursor is called a zymogen (or a proenzyme). A energy source (ATP) is not needed for cleavage. Therefore, in contrast with reversible regulation by phosphorylation, even proteins located outside cells can be activated by this means. You can recognize most zymogens by their name.
Enzymes that begin with 'pro-' or end with '-gen' are often the zymogen form.
For example: PROthrombin is the zymogen form of thrombin, an enzyme involved in blood clotting.
PepsinoGEN is the zymogen form of pepsin, the enzyme found in your stomach that helps digest food.
Why synthesized in inactive form :
Zymogens also ensure the enzyme folds properly To prevent unwanted protein digestion make the enzyme stable in unfavorable environments, and allow the enzyme to go to the proper place so that it doesn't function where it's not supposed to.
How they are activated : Dorka Beri, Asst. Prof. In Biochemistry, GCW (A), Guntur
When the bonds are cut, the enzyme changes its conformation, so that the active site is free or able to become active.
Where are they ? They are mostly found in acinar cells. Acinar cells are cells found in the pancreas and salivary glands . Inside the cells of pancreas and salivary glands, there are proteases that can activate digestive enzymes.
To make sure the proteases inside the cell can't change into the zymogen form before they are released into your digestive system, the cell uses special holding rooms called granules.
Zymogen granules are places in the cell that keep zymogens safe from the proteases inside the cell. They are like little rooms, or little bubbles, full of different types of zymogens.
Accumulate at the apex of Acinar Cells
Due to the signal or nerve impulse, they are released into the gastro- intestinal tract.
How are they activated ? Zymogens can be activated by proteases that cut the amino acid bonds. They can also be activated by the environment and become autocatalytic. Autocatalysis is self-activation and happens when something in the environment allows the zymogen to cut its own chemical bonds. Pepsinogen, for example, does not become pepsin until the pH is around 2- 3. The extra hydrogens found in the lower pH makes the molecule cut its own bonds and become active enzyme.
Sum up :
Known as proenzymes or Zymogens Dorka Beri, Asst. Prof. In Biochemistry, GCW (A), Guntur
Inactive precursors of enzyme
ATP not required for activation
Zymogen activation is irreversible
EX :
Zymogen Active form of ( Inactive form of Enzyme Enzyme ) pepsinogen pepsin Trypsinogen Trypsin Chymotrypsinogen Chymotrypsin Procarboxy peptidase Carboxy peptidase Pro-elastase Elastase plasminogen plasmin Pro-thrombin Thrombin Fibrinogen Fibrin Pro-Insulin Insulin
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