CATALYTIC PROPERTIES AND CHEMICAL-COMPOSITION OF PEPSINS FROM ATLANTIC COD (GADUS-MORHUA)

1. 1. Three pepsin were purified from the gastric mucosa of Atlantic cod (Gadus morhua). 2. 2. The enzymes, called Pepsin I and Pepsin IIa and b, had isoelectric points 6.9, 4.0 and 4.1, respectively, and digested hemoglobin at a maximal rate at a pH of approximately 3. 3. 3. They resembled bovine cathepsin D in being unable to digest the mammalian pepsin substate N-acetyl-l-phenylalanyl-3,5-diiodo-l-tyrosine. 4. 4. Specificity constant (kcat/Km) for the cod pepsin were lower than for porcine pepsin, and they expressed higher substrate affinity and physiological efficiency at pH 3.5 than at pH 2. 5. 5. The cod pepsin are glycoproteins, and their amino acid composition resembles that of porcine cathepsin D more than that of porcine pepsin. 6. 6. The N-terminal sequence of Atlantic cod pepsin is substantially different from that of porcine pepsin. This indicates a significant evolutionary gap between fish and mammalian pepsins. © 1990.