These cells produce pepsin, which breaks down proteins

The cells that produce pepsin, an enzyme that breaks down proteins during the digestive process is Chief cells.  Pepsin is the main digestive enzyme in the stomach that breaks down proteins. Pepsin is produced by the chief cells in the inactive form pepsinogen, which is then converted to pepsin by the hydrochloric acid from the parietal cells. 

Active site is where they touch.

Because the carnivores keep the herbivore population in check