PANCREATIC ENZYMES PARTICIPATE IN THE DEGRADATION OF INTESTINAL SUCRASE-ISOMALTASE

Abstract

The pancreatic ducts were by-passed with a catheter placed within the common bile duct in order to prevent the entry of pancreatic enzymes into the duodenum without interrupting bile flow. For eight days, rats were fed a diet (peptones, sucrose, coconut oil, vitamins and minerals) that could be digested without pancreatic enzymes. Control animals were sham operated and pair fed with the same diet. Relative rates of synthesis and degradation were estimated by pulse labelling and double labelling respectively, for sucrase and for total protein, in total intestinal mucosa and along the gradient of cells collected from the tip of the villus to the bottom of the crypt. The rate of degradation of sucrase was 1.7 times higher than that of total protein in controls, whereas in experimental animals it was equal to that of total protein. This change in rate of degradation produced a proportional increase of sucrase activity in experimental animals. The effect of pancreatic enzymes on sucrase was apparent along the entire length of the villus but not in the crypt. These data support the hypothesis that pancreatic proteases release sucrase-isomaltase from the brush-border membrane, resulting in the observed increase of the rate of degradation. Electrophoretic separation of immunoprecipitated sucrase-isomaltase showed that the intact pro-sucrase-isomaltase observed in operated animals is split into two subunits (sucrase and isomaltase) by the action of pancreatic proteases in control animals. Supported in part by grant # 1 T32 HD 07266-01 NIH