Proteolytic enzymes of pancreas
1. Pancreatic juice is a colorless, odorless, watery secretion isosmotic with that of plasma.
2. About 1-1.5 liters of pancreatic juice is secreted in 24 hours. pH is 8-9, specific gravity is 1.010 - 1.018
- Water – 99%
- Solids – 1%
- Both organic and inorganic substances.
a. Inorganic substances:
- HCO3 concentration → 135-140 mEq/L (increases with increased rate of secretion)
- Cl- concentration → 10-15 mEq/L (inversely related to HCO3 concentration)
- Na++ → 130 mEq/L
- K+ → 10-15 mEq/L
b. Organic constituents:
- Trypsin inhibitor
4. The following enzymes of the pancreatic juice are as follows:
- Procarboxy peptidase
Proteolytic enzymes are secreted in inactive state. The inactive granules are activated in the duodenum where they act on various proteins.
It is a long polypeptide chain with molecular weight 25,000 and has 229 amino acids. Cleavage between 5th and 6th amino acid produces trypsin. Activation by acid, enterokinase, MgSO4, CaCl3 and trypsin itself. Trypsin acts on polypeptide bonds located in the interior of proteins molecules. Therefore it is an endopeptidase.
Molecular weight is 25,700 and has 248 amino acids. Cleavage between the 15th and 16th amino acids produces chymotrypsin. It is also an endopeptidase. Activated by trypsin and enterokinase. Specially acts on peptide whose carboxyl groups are provided with tyrosine and phenylalanine.
Activated to carboxy peptidase A by trypsin. It acts on terminal peptide bonds of end products of chymotrypsin and elastase digestion.
Activated to carboxy peptidase B by trypsin. It acts on C terminal peptide bonds of the end products of trypsin digestion. These two enzymes are exopeptidases as they act from the end of the molecules. The end products of all these enzymes are dipeptides, tripeptides and amino acids.
It is activated by trypsin to elastase and causes digestion of elastin and other polypeptides.