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Related Experiment Videos

Postinsertional processing of sucrase-alpha-dextrinase precursor to authentic subunits: multiple step cleavage by

G L Shapiro1, S D Bulow, K A Conklin

  • 1Department of Medicine, Stanford University School of Medicine, California 94305.

The American Journal of Physiology
|November 1, 1991
PubMed
Summary

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The pancreatic protease trypsin is crucial for cleaving the sucrase-alpha-dextrinase precursor (P) into its active alpha- and beta-subunits in the intestinal brush border. This process involves differential trimming, yielding more beta-subunit than alpha-subunit.

Area of Science:

  • Biochemistry
  • Gastroenterology
  • Molecular Biology

Background:

  • Sucrase-alpha-dextrinase is synthesized as a single-chain precursor (P) and transported to the intestinal brush border.
  • The conversion of P to its active alpha- and beta-subunits is essential for carbohydrate digestion.
  • Previous attempts to replicate this conversion under controlled conditions were unsuccessful.

Purpose of the Study:

  • To elucidate the specific proteases involved in the post-insertional cleavage of the sucrase-alpha-dextrinase precursor (P).
  • To understand the mechanism and conditions required for the conversion of P to its functional subunits.

Main Methods:

  • In vivo radiolabeling of rats with [3H]leucine or [35S]methionine to trace protein synthesis and processing.
  • Immunoprecipitation of sucrase-dextrinase from intestinal brush borders under various conditions (e.g., absence/presence of biliary-pancreatic secretions).

Related Experiment Videos

  • In vitro incubation of isolated brush borders with pancreatic proteases and kinetic analysis using brush-border vesicles.

    • Main Results:

    • The precursor P is only converted to alpha- and beta-subunits after the restoration of intestinal flow and the presence of biliary-pancreatic secretions.
    • Trypsin, a pancreatic protease, was identified as the sole enzyme responsible for converting P to authentic alpha- and beta-subunits.
    • The conversion process involves intermediate species and differential cleavage, resulting in a higher molar ratio of beta-subunit to alpha-subunit (0.77).

    Conclusions:

    • Trypsin is both necessary and sufficient for the processing of the sucrase-alpha-dextrinase precursor (P) into its active subunits.
    • The conversion is a complex, multi-step process involving differential proteolytic trimming, not a single cleavage event.
    • This mechanism ensures the efficient production of functional sucrase-alpha-dextrinase for intestinal carbohydrate digestion.