Isolation and characterization of gastric proteases from the Greenland cod (Gadus ogac)

• Main Author: Squires, E. James
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1984
• Subjects: Arctic; Greenland; Gadus ogac; Greenland cod; North Atlantic
• Online Access: https://research.library.mun.ca/4060/; https://research.library.mun.ca/4060/1/Squires_EliJames.pdf; https://research.library.mun.ca/4060/2/Squires_EliJames.pdf

The Greenland cod Gadis ogac is a sub-arctic species that thrives year round in the North Atlantic. It is postulated that the gastric proteases of this fish have several properties in common with the gastric proteases from mammalian species but also have several characteristics unique to fish species. Therefore, the gastric proteases and their zymogens were isolated from the stomach mucosa of the Greenland cod Gadus ogac and their properties compared to mammalian gastric proteases and the gastric proteases of other fish. Attempts were also made to purify porcine pepsin A and porcine gastricsin from a crude commercial pepsin preparation. The properties of the purified gastricsin fraction obtained differed substantially from the literature data on porcine gastricsin so that direct comparisons of many of the properties of gastricsin and the cod proteases could not be made. -- The zymogens of three gastric proteases were separated and purified by Sephadex G100 chromatography at pH 7, chromatofocusing and, after activation of the zymogens, Sephadex G75 chromatography at pH 2.5. The zymogens of protease 1, 2, and 3 had isoelectric points of > 7.5, 6.2 and 5.2 respectively. The zymogens of the Greenland cod gastric proteases were activated much more rapidly at low temperature than porcine pepsinogen. All three of the cod proteases had more alkaline pH optima with protein substrates than porcine pepsin, especially with methylated protein substrates. The pH optima of cod protease 2 and 3 and porcine pepsin with peptide substrates were all near pH 2 while the pH optimum of cod protease 1 with APDT was near pH 3. The specific activities of the individual cod proteases at 26 °C with protein substrates were generally lower than porcine pepsin. However, a mixture of the cod proteases had activity with the protein substrates that was greater than the sum of the activities of the individual proteases. Cod protease 2 and 3 were active on a number of peptide substrates that are good substrates for gastricsin while cod protease ...