Abstract

To the extent that invertebrates had been investigated in the past, it appeared that they possessed an extracellular proteolytic digestive enzyme complement comparable to that found in vertebrates. With pepsin as the exception, trypsin, chymotrypsin, carboxypeptidases A and B and various aminopeptldases and dipeptidases were considered to be present. More recently, there have been a number of studies on decapod crustaceans including the crab, lobster, shrimp, and especially the crayfish, which suggest that the complement of proteolytic digestive enzymes is in part comparable to that invertebrates, but that the complement differs in several respects. Trypsin has been isolated and characterized extensively. Crustacean trypsin is exceedingly stable at physiological pH which may be of adaptive value. In contrast, chymotryptic activity, as examined in the crayfish, shrimp, and lobster, has not been demonstrated. Exopeptidases (carboxypeptidases A and B) comparable to those of vertebrates appear to be involved in the digestive process. At least one additional endopeptidase has been isolated from the crayfish, which is not comparable to any of the vertebrate digestive proteinases. The endopeptidase may function in a compensatory manner for the absence of peptic and chymotryptic endopeptidases.

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