proteolytic enzymes
Meaning of proteolytic enzymes: Built as harmless precursors and switched on only in the right place, because a cell that made them active would digest itself.
Definition of proteolytic enzymes
Proteolytic enzymes are proteins that cut other proteins apart by breaking the bonds joining their building blocks. They operate throughout the body, not only in digestion: they release hormones from inactive precursors, drive blood clotting, dismantle worn-out proteins inside cells, and carry out the controlled destruction of unwanted cells. The digestive ones are simply the most familiar, because they work in bulk in the gut.
How does a cell avoid digesting itself?
By never building the working form in the first place. A cell that made active trypsin inside itself would destroy its own machinery, so these digestive enzymes are manufactured and stored as inert precursors, each carrying a short blocking segment across its cutting site. Switching one on requires another cut, and that happens outside the cell. In the small bowel an enzyme anchored to the intestinal lining converts trypsinogen into trypsin, and trypsin then activates the rest of the batch, including more of itself. One switch thrown in a safe place turns on the whole set. The gland adds a further safeguard by making an inhibitor that neutralizes any trypsin activated too soon.
Where do they work?
| Location | Examples | Job |
|---|---|---|
| Stomach | Pepsin | Starts breaking down food protein in acid |
| Small bowel | Trypsin, chymotrypsin | Finishes the digestion of food protein |
| Blood plasma | Thrombin and the clotting cascade | Builds clots and later dissolves them |
| Inside every cell | Cathepsins, the proteasome | Recycles damaged and surplus protein |
| Tissue spaces | Matrix metalloproteinases | Remodels the scaffolding between cells |
Only the first two rows concern digestion. Defining the whole class by the pancreas, as older sources do, omits most of what these enzymes actually do.
What happens when the control fails?
Acute pancreatitis is the clearest illustration. When the precursors switch on inside the pancreas instead of in the bowel, the gland begins digesting itself and the fat around it, producing severe pain and inflammation. The opposite failure matters too. If too little reaches the bowel, as in cystic fibrosis or long-standing pancreatic damage, protein and fat pass through undigested, and replacement pancreatic enzyme preparations are taken with meals. Elsewhere, unrestrained cutting of the scaffolding between cells helps tumors invade, and runaway activation of the clotting cascade consumes its own components until bleeding follows. Supplements sold as systemic enzyme therapy rest on the claim that swallowed enzymes reach the blood intact, which sits awkwardly against the fact that proteins taken by mouth are broken down by the enzymes already waiting there.
Also known as
Used in a sentence
Stool testing suggested reduced output of proteolytic enzymes from the pancreas.
Good to know
Proteolytic enzymes are built as inactive precursors and switched on only after leaving the cell, and premature activation inside the pancreas is what makes acute pancreatitis an episode of the gland digesting itself.
Word origin
Where “proteolytic enzymes” comes from
The name joins protein, from the Greek protos meaning first, to lysis, Greek for a loosening or breaking apart. A proteolytic enzyme is one that loosens a protein into pieces.