Chymotrypsin dietary endopeptidases

This discussion of the metalloexopeptidases has focused on the general role of these enzymes in the conversion of dietary proteins into amino acids. In particular, the apparent synergistic relationship which the pancreatic carboxypeptidases have with the major endopeptidases, trypsin, chymotrypsin, and pepsin, in order to facilitate formation of essential amino acids has been stressed. The chemical characteristics, metalloenzyme nature, and mechanistic details of a representative of each class of exopeptidase have been presented. Leucine aminopeptidase from bovine lens was shown to be subject to an unusual type of metal ion activation which may be representative of a more general situation. Carboxypeptidase A of bovine pancreas was discussed in terms of its three-dimensional structure, the implications of x-ray crystallography to mecha ... 

Trypsin, chymotrypsin, and elastase are serine proteases (see Chapter 9) that act as endopeptidases. Trypsin is the most specific of these enzymes, cleaving peptide bonds in which the carboxyl (carbonyl) group is provided by lysine or arginine (see Fig. 37.3). Chymotrypsin is less specific but favors residues that contain hydrophobic or acidic amino acids. Elastase cleaves not only elastin (for which it was named) but also other proteins at bonds in which the carboxyl group is contributed by amino acid residues with small side chains (alanine, glycine, or serine). The actions of these pancreatic endopeptidases continue the digestion of dietary proteins begun by pepsin in the stomach. 

The first enzymes to act on dietary proteins are the endopeptidases pepsin in the gastric juice and trypsin, chymotrypsin and elastase secreted by the pancreas into the small intestine. (The different specificities of trypsin, chymotrypsin and elastase are discussed in section 2.2.1.)... 

The human organism is not able to use dietary proteins as such. They must be hydrolysed into single amino acid molecules before they can be absorbed. The hydrolysis of proteins (mostly denatured proteins) is catalysed by proteolytic enzymes called proteases (proteinases or peptidases), which have relatively high substrate specificity. They catalyse the hydrolysis of interior peptide bonds to form peptides of different sizes (endopeptidases such as pepsin, trypsin and chymotrypsin) or attack the terminal amino acids (exopeptidases). Hydrolysis of the N-terminal amino acids is... 

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