Pancreatic Enzymes

Overview

• Pancreatic enzymes
  • pancreas secretes enzymes required for digestion of carbohydrates, proteins, and lipids
    • carbohydrates
      • pancreas secretes α-amylase in active form
        • digests 1,4-glycosidic bonds of carbohydrates (starch)
    • lipids
      • lipase-colipase
        • pancreas secretes (active) lipase
          • hydrolyzes triglycerides → 1 monoglyceride + 2 fatty acids
          • lipase is inactivated by bile salts
          • pancreas secretes (inactive) procolipase
            • in intestinal lumen, trypsin activates procolipase
              • procolipase (inactive) → colipase (active)
            • colipase displaces inhibitory bile salts 
              • permits digestive functions of lipase
      • phospholipase A2
        • pancreas secretes (inactive) phospholipase A2
          • in intestinal lumen, trypsin activates phospholipase A2
        • hydrolyzes phospholipids → lysolecithin + fatty acids
    • proteins
      • pancreas secretes proteases in inactive forms called proenzymes/zymogens
        • trypsinogen 
        • chymotrypsinogen
        • proelastase
        • procarboxypeptidase A/B
      • activation of pancreatic proteases
        • brush-border enterokinase/enteropeptidase activates trypsinogen 
          • trypsinogen (inactive) → trypsin (active)
        • trypsin catalyzes conversion of inactive precursors to active enzymes
          • trypsinogen → trypsin (positive feedback loop) 
          • chymotrypsinogen → chymotrypsin
          • proelastase → elastase
          • procarboxypeptidase A/B →carboxypeptidase A/B
      • pancreatic proteases hydrolyze dietary protein to absorbable molecules
        • amino acids, dipeptides, tripeptides