Trypsin RIA

Trypsin is one of the enzymes involved in the digestion of dietary protein in the small bowel. It functions as an endopeptidase with a marked preferential specificity for peptide bonds arising from the carbonyl groups of Larginyl and L-lysyl residues. Chemically, trypsin is a protein consisting of 201 amino acids with a molecular weight of 22,900 Da. In common with other proteolytic enzymes of pancreatic origin, trypsin is synthesized and secreted from the acinar cells of the exocrine pancreas as an inactive precursor or proenzyme, trypsinogen. This occurs in two forms, both of which are converted to enzymatically active trypsin by the action of enterokinase produced by cells in the duodenum. This kinase, in the presence of Ca++ ions, removes the hexapeptide Val (Asp)4-Lys from trypsinogen, thereby unmasking the active center of the trypsin molecule. In addition trypsin itself can activate the trypsinogen by autocatalysis. Some trypsin appears to be excreted intact from the gut, as it can be detected and measured in stool. In addition, the trypsinogen, trypsin and probably trypsin bound to a pancreatic inhibitor may find their way from the pancreatic cells into the blood via the interstitial fluid. In blood all tryptic activity is blocked by three specific inhibitors (α1-antitrypsin, α2-macroglobulin and inter-α-trypsin inhibitor). Nevertheless, normal serum still retains some proteolytic activity as shown by the hydrolysis of synthetic substrates, but this cannot be due solely to trypsin.