Gastric secretion proteolytic enzymes

Gastric secretion represents a very complex naixture of electrolytes, water, carbohydrates, proteins, peptides, and amino acids, which are partly in solution and partly in more or less stable suspension. The large molecular materials of gastric secretion include enzymes, mucosubstances, serum proteins, peptides and products of proteolytic degradation of gastric proteins and mucoproteins, and blood group substances. 

Pepsinogen. This precursor of the proteolytic enzyme pepsin is secreted by gastric parietal cells pepsinogen activities may be increased following peptic ulceration and by parasitic infections. The enzyme may be measured in plasma or gastric fluid using colorimetric, fluorimetric, or radioimmunometric methods and ELISA methods (Will et al. 1984 Ford et al. 1985 Tani et al. 1987 Lynch et al. 2004). 

Proteins are digested in the stomach and intestine under the influence of proteolytic enzymes. The stomach contains at least two enzymes— pepsin and renin— which are secreted by the mucosal cells in the form of zymogens. The gastric cell secretes pepsinogen, a long polypeptide molecule with no catalytic property. Pepsin is activated to pepsinogen within the gastric lumen under the influence of at least two factors the low pH of the medium, which is a result of hydro-... 

There are two main classes of proteolytic digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolyzed. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. They are the first enzymes to act, yielding a larger number of smaller fragments, eg, pepsin in the gastric juice and trypsin, chymotrypsin, and elastase secreted into the small intestine by the pancreas. Exopeptidases catalyze the hydrolysis of peptide bonds, one at a time, fi"om the ends of polypeptides. Carboxypeptidases, secreted in the pancreatic juice, release amino acids from rhe free carboxyl terminal, and aminopeptidases, secreted by the intestinal mucosal cells, release amino acids from the amino terminal. Dipeptides, which are not substrates for exopeptidases, are hydrolyzed in the brush border of intestinal mucosal cells by dipeptidases. 

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