Pepsin

• Globular, water soluble, large polymers joined by peptide-bonds, it must be stored at low temperatures (-50°C to -20°C) to prevent self-digestion, its tertiary structure is held together by H-bonds and 2 disulphide bridges
• 43 amino acids with acidic R-groups (to be stable in the stomach’s acidic environment), very few amino acids with basic R-groups (4); to accept H^+ ions (little effect on enzyme structure)
• The single polypeptide chain of 327 amino acids folds into a tertiary symmetrical structure; it digests proteins in the stomach (proteolytic enzyme)