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Investigation of proteinases in the digestive tract using 4-methoxy-2-naphthylamine (MNA) substrates
Abstract:
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.
Insights
This study investigated digestive tract proteinases and ester proteinases in rodents. Enzyme activity and localization varied by organ and sex, suggesting specialized cellular functions.
Area of Science:
- Biochemistry
- Histochemistry
- Gastroenterology
Background:
- Digestive tract proteinases and ester proteinases play crucial roles in physiological processes.
- Understanding their distribution and activity is essential for comprehending digestive functions.
Purpose of the Study:
- To investigate the biochemical and histochemical characteristics of various proteinases and ester proteinases in the rodent digestive tract.
- To identify organ-specific and sex-specific differences in enzyme activity and localization.
Main Methods:
- Biochemical assays using 4-methoxy-2-naphthylamine (MNA) substrates and ester proteinases with n-acetyl-L-methionine-1-naphthylester.
- Histochemical localization of enzymes within digestive tract cells and tissues.
Main Results:
- Proteinase and ester proteinase activities varied significantly across different digestive organs (salivary glands, esophagus, stomach, liver, pancreas, intestines, colon).
- Distinct sex differences in enzyme activity were observed, particularly in the submandibular glands of rats and mice.
- Enzymes were localized to specific cellular compartments, including surface membranes, lysosomes, secretion granules, and the Golgi apparatus, with cell-type specific enzyme profiles identified.
Conclusions:
- Proteinases and ester proteinases exhibit diverse activities and specific cellular localizations within the digestive tract.
- These enzymes are likely involved in specialized functions of various cell types, including endocrine, exocrine, resorptive, and immune cells.
- The findings highlight the complex enzymatic machinery of the digestive system and its potential role in organ-specific and sex-influenced physiological processes.