Evidence of degradation process of sucrase-isomaltase in jejunum of adult rats.
To evaluate degradation processes of sucrase-isomaltase in adult rat jejunum, we determined enzymic activity of sucrase and isomaltase and compared it with the amount of immunoreactive sucrase-isomaltase. In rats fed or starved for 18h, killed at 10:00 h or 22:00 h, sucrase activity (expressed on the basis of total protein or of immunoreactive sucrase-isomaltase) was significantly (P less than 0.02) lower in the lower jejunum than in the upper jejunum; isomaltase activity was similar in both segments. Crossed immunoelectrophoresis demonstrated the existence of a second sucrase-isomaltase antigen reacting with anti-(sucrase-isomaltase) serum. This antigen was present in larger amounts in the lower jejunum than in the upper jejunum, exhibited immunological partial identity with the intact sucrase-isomaltase, and had isomaltase activity but no sucrase activity. Results suggest that this antigen is a degradation product of sucrase-isomaltase in which the sucrase active site has been broken down. To examine the role of pancreatic enzymes in degradation of sucrase-isomaltase, common pancreatico-biliary ducts were ligated. Within 18 h after the operation, the difference of sucrase activity between the upper and the lower jejunum disappeared and the amount of the second sucrase-isomaltase antigen markedly decreased in the lower jejunum. Our results indicate that, during the degradation of intestinal sucrase-isomaltase by the pancreatic proteinases, degradation of the sucrase active site precedes that of the isomaltase active site.
D000818:Animals; D000941:Antigens / Q000032:analysis; D001659:Biliary Tract / Q000378:metabolism; D001665:Binding Sites; D007123:Immunoelectrophoresis, Two-Dimensional; D007583:Jejunum / Q000201:enzymology* / Q000276:immunology; D009097:Multienzyme Complexes / Q000378:metabolism*; D009834:Oligo-1,6-Glucosidase / Q000378:metabolism; D010179:Pancreas / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013393:Sucrase / Q000378:metabolism; D013394:Sucrase-Isomaltase Complex / Q000276:immunology / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism
D000941:Antigens; D009097:Multienzyme Complexes; D013394:Sucrase-Isomaltase Complex; D009834:Oligo-1,6-Glucosidase; D013393:Sucrase; D014357:Trypsin