Trypsin is a proteolytic enzyme secreted by the pancreas that works optimally at alkaline pH (7.5–8.5) in the small intestine. Pepsin works in strongly acidic conditions (pH 1.5–2). The alkaline environment of the duodenum (neutralized by pancreatic bicarbonate) is optimal for pancreatic enzymes including trypsin, chymotrypsin, and lipase.