95. IN VITRO EFFECTS OF PANCREATIC PROTEASES ON P PRECURSOR OF RAT INTESTINAL SUCRASE-ISOMALTASE (S-I)

Abstract

Pancreatic proteases are known to be involved in the cleavage of the P precursor of S-I in its two subunits S and I after its insertion to the brush-border (BB) membrane. The aim of this study was to determine in vitro the respective role of trypsin (T) and elastase (E) in this post-insertional process. Duodenum biliary-pancreatic attachments were transposed in rat (DT) to ileum leaving the jejunum devoid of these secretions. One month after surgery, DT and control rats (C) received 5mCi 35S-methionine IP and were killed 5hrs latter. SI-immuno electrophoresis from jejunal BB revealed only P in DT and S and I in C. BB of DT (250μg) were incubated with E (5-20mU/ml) or T (100-5000mU/ml) for 30 and 60mn at 37°C. E induced a major solubilization of P, a poor cleavage of P in 2 abnormal bands and an inactivation of S and I activities. T, for 30mn, cleaved P in normal I and S. 60mn incubation resulted in the apparition of a 3rd band I' (MW:I>I'>S). A solubilization of the cleaved S and I was also observed. Our results suggest that, besides the solubilization role of E and T, T is the main pancreatic enzyme implicated in the normal cleavage of P in its 2 sub-units I and S and in the obtention of the normal balance between S and I activities. Depending of pancreatic protease concentrations in the digestive lumen in vivo, abnormal physiological S-I sub-units should be found.