An enzyme functional only in an acidic medium is _______.

Pepsin, the important gastric enzyme, is most active at a pH of 2.0 to 3.0 and is inactive at a pH above about 5.0. Consequently, for this enzyme to cause digestive action on protein, the stomach juices must be acidic. Pepsin initiates the process of protein digestion, usually providing only 10 to 20 per cent of the total protein digestion to convert the protein to, proteoses, peptones, and a few polypeptides. This splitting of proteins occurs as a result of hydrolysis, at the peptide linkages between amino acids.