What are the differences between pepsin and pepsinogen?

Pepsin and pepsinogen are two closely related proteins that play important roles in the digestion of proteins in the stomach. Here are the key differences between pepsin and pepsinogen:

1. Function:

- Pepsin: Pepsin is an active enzyme that breaks down proteins into smaller peptides. It works in the acidic environment of the stomach.

- Pepsinogen: Pepsinogen is an inactive precursor of pepsin. It is secreted by the chief cells of the stomach in response to the presence of food.

2. Activation:

- Pepsin: Pepsinogen is activated into pepsin by the acidic environment of the stomach. The hydrochloric acid (HCl) secreted by the parietal cells of the stomach converts pepsinogen into pepsin.

- Pepsinogen: Pepsinogen itself does not require activation. It is converted into pepsin when the pH of the stomach drops to around 1.5-2.0.

3. Location:

- Pepsin: Pepsin is found in the gastric juice, which is the acidic fluid secreted by the stomach.

- Pepsinogen: Pepsinogen is produced by the chief cells of the gastric glands in the stomach. It is stored in the inactive form within the secretory granules of these cells until needed.

4. pH Requirements:

- Pepsin: Pepsin has an optimal pH range of 1.5-2.0 for its enzymatic activity. It works best in the highly acidic environment of the stomach.

- Pepsinogen: Pepsinogen is stable at neutral pH but is activated by the acidic conditions in the stomach.

5. Proteolytic Activity:

- Pepsin: Pepsin is a protease, which means it specifically cleaves peptide bonds in proteins. It primarily breaks down proteins into smaller peptides by hydrolyzing the peptide bonds between aromatic amino acids (such as phenylalanine, tyrosine, and tryptophan) and acidic amino acids (such as aspartic acid and glutamic acid).

- Pepsinogen: Pepsinogen does not have any proteolytic activity. It is the inactive precursor of pepsin.

In summary, pepsin is the active enzyme responsible for breaking down proteins in the stomach, while pepsinogen is its inactive precursor. Pepsinogen is activated into pepsin by the acidic environment of the stomach, allowing for efficient digestion of proteins in the gastric phase of digestion.