Catheptic endopeptidases and protein digestion in the horse clam Tresus capax (gould)

Abstract

1. 1. The investigation of protein hydrolysis by gastric and digestive diverticular extracts of Tresus, over a wide pH range, indicates that acid proteinases are the most important enzymes. 2. 2. The acid endopeptidases have similar characteristics to vertebrate cathepsins B and D. 3. 3. Cathepsin B occurs in the cells of the digestive diverticula and in the gastric juice, and has a digestive role. 4. 4. Cathepsin D is intracellular in the digestive diverticula and probably has a primary role which is non-digestive. 5. 5. Cathepsins A and C, acid exopeptidases, are also present in the digestive diverticula. 6. 6. A chymotrypsin is found intracellularly in the digestive diverticula. 7. 7. A trypsin is found in the gastric juice. 8. 8. Carboxypeptidase A and leucine aminopeptidase are present. 9. 9. Cathepsin B diminishes in winter when there is little food available, while cathepsin D persists. 10. 10. The intracellular proteolytic capacity of the digestive diverticula is approximately four times that of the stomach.