Investigation of proteinases in the digestive tract using 4-methoxy-2-naphthylamine (MNA) substrates.

Aminopeptidase (AP) A, B, and M, gamma-glutamyltranspeptidase (GGT), endopeptidase I and II, membrane-associated endopeptidase I and II, dipeptidylaminopeptidase (DAP) I, II, and IV, trypsin and chymotrypsin were investigated with 4-methoxy-2-naphthylamine (MNA) substrates and ester proteinases with n-acetyl-L-methionine-1-naphthylester as substrate in the digestive tract of laboratory rodents. Biochemically, proteinases and ester proteinases show different activities in the salivary glands, esophagus, stomach, liver, pancreas, duodenum jejunum, ileum, and colon; sex differences in proteinase and ester proteinase activity were measured, especially in the submandibular gland of rats and mice. Histochemically these enzymes are preferentially localized in surface membranes, lysosomes, secretion granules, and Golgi apparatus of cells of the endocrine and exocrine secretory system, resorptive system and immune system of the digestive tract. Besides the general occurrence of lysosomal (DAP I and II, single cell types and functional units of these systems possess their own individual proteinase and ester proteinase equipment. The cells of the granulated tubules of rat and mouse submandibular gland contain endopeptidase I and ester proteinases, its acinar cells DAP IV, the chief cells of the stomach APA, enteroendocrine cells APA, APM, and DAP II, hepatocytes DAP IV or GGT and DAP IV, lymphocytes GGT and DAP IV, and enterocytes trypsin, chymotrypsin, and membrane-associated endopeptidase I and II. Sex differences in proteinase activity are most conspicuous in the granulated tubule cells of the rat and mouse submandibular gland. The data suggest that proteinases and ester proteinases are involved in specific functions of the cells of the digestive tract. Furthermore, myoepithelial cells, smooth muscle cells of the muscular layer of the stomach and intestine, connective tissue cells (including mast cells) and fibers, nerve cells of the myenteric plexus and the capillary bed of the digestive organs are equipped with some of these proteinases and with ester proteinases and show organ differences.