Characterization of degradation process of sucrase-isomaltase in rat jejunum with monoclonal-antibody-based enzyme-linked immunosorbent assay.
As shown previously, during degradation of sucrase-isomaltase in rat jejunum, degradation of the sucrase active site occurs before that of isomaltase active site [Goda & Koldovský (1985) Biochem. J. 229, 751-758]. To characterize further the process of sucrase-isomaltase degradation in jejunum, we determined the amounts of immunoreactive sucrase-isomaltase in rat jejunum by using a monoclonal-antibody-based enzyme-linked immunosorbent assay. By employing two alternative monoclonal antibodies (one reacting with the sucrase subunit and the other reacting with the isomaltase subunit), the amount of antigen-containing sucrase subunit and the amount of antigen-containing isomaltase subunit were separately quantified. In both upper and lower jejunum of rats, the amount of antigen-containing isomaltase subunit was always higher than the amount of antigen-containing sucrase subunit. This difference was attributable mainly to a degradation product of sucrase-isomaltase, which was identified as isomaltase monomer. Occlusion of pancreatic ducts for 18 h eliminated the difference between the amount of antigen-containing sucrase subunit and the amount of antigen-containing isomaltase subunit in both upper and lower jejunum. In jejunum of control animals, the molar ratio of sucrase subunit to isomaltase subunit was estimated to be 0.32-0.52, indicating that quite a large proportion of sucrase-isomaltase (48-68%) is present as degradation products (e.g. isomaltase monomer). These results support the model of degradation process of sucrase-isomaltase in brush-border membranes of rat jejunum, whereby degradation of sucrase subunit by the action of pancreatic proteinase(s) precedes degradation of isomaltase subunit.
Goda
T
T
Department of Pediatrics and Physiology, University of Arizona College of Medicine, Tucson 85724.
Quaroni
A
A
Koldovský
O
O
D000818:Animals; D000911:Antibodies, Monoclonal; D002850:Chromatography, Gel; D004797:Enzyme-Linked Immunosorbent Assay; D007583:Jejunum / Q000201:enzymology*; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism*; D010182:Pancreatic Diseases / Q000201:enzymology; D010183:Pancreatic Ducts; D051381:Rats; D011919:Rats, Inbred Strains; D013394:Sucrase-Isomaltase Complex / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D009097:Multienzyme Complexes; D013394:Sucrase-Isomaltase Complex