Why pepsin required an acidic medium to break down protein?

Pepsin, a protease enzyme, requires an acidic medium to break down proteins because it is most active in this specific environment. Here are the reasons why an acidic medium is essential for pepsin's function:

1. Optimal pH for Activity: Pepsin has an optimal pH range between 1.5 and 2.5, which is highly acidic. At this pH, pepsin's catalytic site and structure are most stable and efficient. The acidic environment provides the necessary conditions for pepsin to bind to and cleave peptide bonds in proteins.

2. Protonation of Substrate: In an acidic medium, the acidic conditions protonate the substrate proteins. This protonation changes the charge of the amino acid residues at the cleavage sites, making them more susceptible to pepsin's enzymatic attack. The protonated substrate proteins become positively charged, which enhances their interaction with pepsin's active site.

3. Activation of Pepsinogen: Pepsin is initially produced in an inactive form known as pepsinogen. The acidic environment in the stomach triggers the conversion of pepsinogen into its active form, pepsin. This activation process involves the removal of an inhibitory peptide from pepsinogen, allowing the enzyme to attain its functional conformation and begin proteolytic activity.

4. Protection from Degradation: The acidic environment in the stomach also serves to protect pepsin from being degraded by other proteases. Most other digestive enzymes, such as trypsin and chymotrypsin, are active in a more neutral or alkaline pH range. The highly acidic conditions in the stomach help preserve pepsin's stability and activity while preventing its denaturation or degradation by other enzymes.

Therefore, an acidic medium is crucial for pepsin's function as it provides the optimal pH for its activity, protonates the substrate proteins, facilitates the activation of pepsinogen, and protects pepsin from degradation in the stomach.