There isn't a single "optimum pH" for peptidase because it's a broad class of enzymes. Different peptidases have different optimal pH ranges depending on their specific function and where they are found in the body.

Here are some examples:

* Pepsin: A stomach enzyme, pepsin works best in a highly acidic environment with an optimal pH of 1.5 to 2.5.

* Trypsin: Found in the small intestine, trypsin has an optimal pH of 7.0 to 8.0, which is slightly alkaline.

* Chymotrypsin: Another small intestine enzyme, chymotrypsin also works best in an alkaline environment with an optimal pH of 7.8 to 8.7.

Important Note: The pH of the environment directly impacts enzyme activity. A pH outside the optimal range can cause the enzyme to lose its structure and function, significantly reducing its effectiveness.

To understand the optimal pH of a specific peptidase, you need to know the specific enzyme and its cellular location.