Pepsin fragmentation

Protein (long peptide chain) Pepsin Fragment proteins into smaller peptides Stomach chief cells Stomach... 

Fig. 6.14. Two dimensional electrophoresis of a mixture of cell surface antigens obtained from lung tissue. Pepsin treatment between the first and second run. A. Healthy tissue B, neoplastic tissue. The arrows denote the presence of unusual pepsin fragments in the preparation from the neoplastic tissue (courtesy of Dr. Svojtkov ).

Sephel, G.C., Tashiro, K., Sasaki, M., Kandel, S., Yamada, Y. and Kleinman, H.K. (1989) A laminin-pepsin fragment with cell attachment and neurite outgrowth activity at distinct sites. Dev. Biol. 135 172-181. 

Figure 2. Human IgG, showing the location of the sites of cleavage of F(ab )s and Fc fragments as well as the Fc (papain) and pFc (pepsin) fragments (numbered from COOH-terminal ends of y chains). Carbohydrate is denoted by Cbh. Reproduced from Turner et al. (1969o) by courtesy of Dr. M. W. Turner and Nature.

JT-Ray studies on the F a fragnients prepared by papain and pepsin fragmentation of human myeloma IgG immunoglobulins are being carried out by Poljak et /. The preparation of heavy-atom derivatives has involved considerable difficulties. A 6A electron-density map has been computed, which shows two clear domains (unpublished work) and is clearly of good quality. The data have been collected to 3.S A resolution, refinement of the heavy-atom positions of the derivatives has been completed, and an electron-density map computed. 

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. 

FAB Fast-electron bombardment Fab Antigen binding fragment F(ab )2 Fragment of an immunoglobulin produced pepsin treatment... 

Pepsinogen is produced by the chief cells. Within the lumen of the stomach, this precursor molecule is split by HCl to form the active enzyme pepsin. Optimally active at an acidic pH (pH = 2), pepsin begins protein digestion by fragmenting proteins into smaller peptide chains. 

Figure 20.10 Digestion of IgG class antibodies with pepsin results in heavy chain cleavage below the disulfide groups in the hinge region. The bivalent fragments that are formed are called F(ab )2. The remaining Fc region normally is severely degraded into smaller peptide fragments.

Figure 20.12 F(ab )2 fragments produced by pepsin digestion of IgG can be reduced at their heavy chain...

F(ab )2 fragments of antibodies are generated by pepsin digestion of whole IgG antibodies to remove a portion of the Fc region (see Sect. 1.1). Elimination of nonspecific binding of the Fc region of antibodies to Fc receptors on cell surfaces in... 

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