Proteolytic digestion and the problem of the pancreas in the ammocoete larva ofLampetra planeri

Abstract

At the anterior end of the intestine 2 types of cells differentiate: (1) follicles are budded off to form the "pancreas," which loses its connection with the gut epithelium and is considered by Cotronei to be a purely endocrine organ; (2) 2 pale patches develop in the gut epithelium which on microscopic examination are seen to consist of cells containing granules giving zymogen reactions, with large vesicular nuclei, and single large nucleoli. Aqueous extracts of tissues tested on gelatine, fibrin and casein showed strong proteolytic activity to be confined to the anterior gut region. The presence of the pancreas was not essential to the production of the enzyme. The optimum pH was at 7.5-7.8, and digestion was carried to the amino acid stage, showing the presence of a tryptic type enzyme. Very weak proteolytic activity was obtained in extracts of gill epithelium, liver and lower intestine, in acid medium, probably due to a cathepsin. The behavior of the protease suggests that of the Tunicate proteases. It is suggested that in the evolution of the pancreas, the endocrine component became separated from the gut before the exocrine.