Evidence of degradation process of sucrase-isomaltase in jejunum of adult rats

Abstract

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.

Effect of Dietary Fat Content on Microvillus in Rat Jejunum.

“…Because sucrase-isomaltase is known to be coded in a single gene (20) and synthesized as a single polypeptide of pro-sucrase-isomaltase (21), the alteration of sucrase to isomaltase activity ratio suggested that sucrase isomaltase was posttranslationally modified by the dietary manipulation. Degrada tion of sucrase-isomaltase was suggested to occur first on the sucrase subunit in the intestinal microvillar membranes (22,23). Therefore, it seems most likely that degradation of sucrase-isomaltase was enhanced in the rats fed the high-fat diet.…”

Hydrolysis of .ALPHA.-D-glucopyranosyl-1,6-sorbitol and .ALPHA.-D-glucopyranosyl-1,6-mannitol by rat intestinal disaccharidases.

“…1). It has been demonstrated that this column efficiently separates sucrose-isomaltase complex and its degradation product, i.e., isomaltase monomer (6,15). The fractions containing sucrase-isomaltase and the fractions containing isomaltase monomer were denoted as peak II and peak III, respectively.…”

Cholestyramine and Bile Diversion Lower the Aminopeptidase Activity in the Intestinal Brush Border Membrane of Rats.

“…As mentioned above, cholestyramine and bile diversion lowered the activities of luminal trypsin and chymotrypsin probably by means of decreased abundance of luminal bile acids. Because the sucrase-active site is degraded by the action of pancreatic proteinases (7,8), it is possible that the increase in sucrase activity with cholestyramine or bile diversion might result from the decrease in degradation by the luminal proteinases. The activity of alkaline phosphatase was increased with cholestyramine but not with bile diversion, so this enzyme may be affected by other factors than the luminal bile acids.…”

“…Evidence from a number of studies showed that some enzymes presented in the intestinal brush border membrane were influenced by the luminal factors (4-11). Goda and Koldovsky (7) reported that the sucrase-active site of sucrase-isomaltase in the small intestine of rat is degraded by the action of pancreatic proteinases. Goda et al (8) showed that the intake of a high-protein, low-carbohydrate diet accelerated the degradation of sucrase-isomaltase by means of the increase of luminal pancreatic proteinases.…”

“…Because the aminopep tidase is embedded within the brush border membrane and most of its domains including the active site are exterior to the cell surface, it is possible that the activity is influenced by some luminal factors, such as pancreatic proteases and bile acids . Other enzymes in the intestinal brush border membrane are known to be influenced by the luminal factors (4)(5)(6)(7)(8)(9)(10)(11).…”