Proteolysis post mortem in North Atlantic krill

Abstract 1. 1. The autoproteolytic processes in selected species of North Atlantic krill, Meganyctiphanes norvegica (M. Sars), Thysanoessa inermis (Kroyer) and T. raschii (M. Sars) have been examined at 0°C by following the release of peptides and free amino acids. 2. 2. The krill contains high levels of peptide hydrolases, and autoproteolysis seems to be due mainly to digestive enzymes localized in the hepatopancreas and the intestinal tract of the animals. 3. 3. During autoproteolysis the individual amino acids were generally released at rates corresponding to their proportion in the bulk protein of the krill. The major exceptions were alanine which accumulated in amounts larger than was to be expected from the composition of the krill protein, and glutamic acid/glutamine, aspartic acid/asparagine, arginine, and to some extent glycine, proline and serine, which accumulated to a lesser extent than was to be expected. 4. 4. Storage of krill for 1 week resulted in only minor changes in the total content of amino acids as determined after acid hydrolysis, with the exception of alanine which increased in concentration. 5. 5. The results suggest that the formation of free alanine is partly due to reactions other than proteolysis. 6. 6. The release of free amino acids was accompanied by a considerable increase in the amount of small peptides, and glutamic acid/glutamine, aspartic acid/asparagine, glycine and proline tended to accumulate in these peptides. 7. 7. The autoproteolytic activity of the Thysanoessa species showed seasonal variations, probably in response to food availability. In the case M. norvegica , the results suggest that there are smaller fluctuations in the level of proteolytic enzymes, probably indicating less pronounced variations in the food intake over the year.