Question

What is pepsinogen?

Answer 1

Pepsinogen is a proenzyme that is present in our stomach. It is converted into pepsin due to a chemical reaction that takes place in the stomach. It secretes pepsin which is needed for digestion of proteins in the body.

Complete answer:
The process of digestion is accomplished by mechanical and chemical processes. The food enters the body through the mouth and passes down into the food pipe. It is then passed down into the stomach. The stomach stores the food for 4-5 hours.
The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of their muscular wall and is called chyme. The proenzyme pepsinogen, on exposure to hydrochloric acid gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach. Pepsin converts proteins and peptones.
The mucous and bicarbonates present in the gastric juice play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid. HCL provides the acidic pH around 18, optimal for pepsins. Small amount of pepsin passes through the stomach into the bloodstream where they break out small or large fragments of proteins that are absorbed by the small intestine. Chronic backflow of pepsin or hcl back into the esophagus from the stomach can cause gastroesophageal reflux diseases.
Pepsinogen consists of a single polypeptide chain that is about approx 42,000 DA. It belongs to the endopeptidase family of aspartic proteinases. The aspartic protease is an acidic protease because it acts in pH between 1.5 and 5. The human lining of the stomach secretes mainly 4 types of pepsinogen which are pepsinogen I, pepsinogen II, cathepsin E and cathepsin D.

Note:
Chief cells are the main source of pepsinogen that inactivates the precursor called pepsin. Pepsin is needed for the digestion of protein in the stomach. Pepsinogen is identified by immunofluorescence in humans as early as 8 week gestation.