Abstract
The S-I complex is synthesized as a single chain precursor P. Once it reaches the brush-border surface, P is split by pancreatic proteases into S and I. Recently, we have documented in vitro this cleavage. Among the proteases tested: trypsin (T), elastase (E) and chymotrypsin (C), T was the only one involved in producing normal S-I. But, depending on the protease and its concentration, abnormal forms of S and I were observed. Thus, to document those observations, modifications of pancreatic enzyme balances in intestinal lumen were induced in rats either physiologically (i.e. by diet changes), either as a result of surgical transfert of pancreatic ducts. By electrophoretic analysis of S-I immunoprecipitates: 1) when T was increased over E and C, an abnormal form of I (I'; mw<I) was found S was inchanged; 2) when E was increased over T or C, two species, E1 and E2, larger than normal S and I, were only observed; 3) when T, E and C, all together were hightly increased, I' and a new specie, S (mw<<S) were the only forms characterized. By both S and I enzyme determinations: 1) all complexes, S-I', E1-E2 and S'-I', indicated a significant decrease in the S/I activity ratio; 2) only the S' species showed an increase of the normal S Km value (24.8 v.s 19.1, p 0.001).
Conclusions: without alterations of the intracellular biosynthetic process, modified S-I complex can be found depending on the luminal environment in pancreatic proteases. Moreover, the observed S'-I' complex, suggests that abnormal function of the exocrine pancreas may induce carbohydrate malabsorption.
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Broyart, JP., Poullain, MG. & Cézard, JP. 49 ABNORMAL SPECIES OF SUCRASE-ISOMALTASE (S-I) ARE ASSOCIATED WITH VARIATIONS OF LUMINAL PANCREATIC ENZYME CONTENT IN RAT INTESTINE. Pediatr Res 24, 413 (1988). https://doi.org/10.1203/00006450-198809000-00072
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DOI: https://doi.org/10.1203/00006450-198809000-00072