Q. What are the zymogens?

proenzymes, or Zymogens, are enzymes secreted in inactive form. Under some conditions a zymogen shifts to the active form of the enzyme. Zymogen secretions in general happen because the enzyme activity can damage the secretory tissue.

For example, the pepsinogen secreted by the stomach becomes active under acid pH turning into the enzyme pepsin. Other well-known zymogens are chymotrypsinogen and trypsinogen, enzymes that are secreted by the exocrine pancreas and which become chymotrypsin and trypsin respectively.