Proteases are enzymes that break down proteins by cutting the chemical bonds holding them together. Every living organism produces them, and they play roles in everything from digesting food to healing wounds to recycling damaged cells. They’re also one of the most commercially valuable enzyme groups, showing up in laundry detergents, meat tenderizers, and pharmaceutical drugs.
How Proteases Work
Proteins are long chains of smaller building blocks called amino acids, linked together by peptide bonds. A protease works by breaking those bonds, splitting a protein into smaller fragments or individual amino acids. This process is called hydrolysis because a water molecule is involved in snapping each bond apart.
Not all proteases cut in the same place. Endopeptidases target bonds in the middle of a protein chain, while exopeptidases work from the ends, snipping off one or two amino acids at a time. Your body uses both types depending on the task. Digestion, for instance, relies on endopeptidases to chop a large dietary protein into manageable pieces, then exopeptidases to trim those pieces down to individual amino acids your intestines can absorb.
Six Classes of Proteases
Scientists classify proteases into six groups based on how they carry out their cutting action: serine, cysteine, threonine, aspartic, glutamic, and metalloproteases. The names come from the specific part of the enzyme that does the work.
Serine, cysteine, and threonine proteases use one of their own amino acid building blocks as the chemical “blade” that attacks the peptide bond. Aspartic, glutamic, and metalloproteases take a different approach, using an activated water molecule to do the cutting instead. Glutamic proteases have not been found in mammals, but the other five classes are active throughout the human body.
Proteases in Digestion
The digestive system is where most people first encounter protease activity, even if they don’t realize it. Protein digestion begins in the stomach with pepsin, the principal enzyme for breaking down dietary protein. Pepsin thrives in the extremely acidic environment of the stomach, working best at a pH of roughly 1.5 to 2. Once food moves into the duodenum (the first section of the small intestine), the pH rises above 6 and pepsin shuts off.
From there, the pancreas takes over. It releases a suite of proteases, including trypsin, chymotrypsin, elastase, and carboxypeptidase, into the small intestine. These enzymes continue breaking protein fragments into amino acids small enough for your intestinal lining to absorb. The handoff between stomach and intestinal proteases is tightly coordinated: each enzyme is tuned to a specific pH range, ensuring protein gets fully dismantled as it travels through the digestive tract.
Roles Beyond Digestion
Proteases do far more than process food. Blood clotting depends on a cascade of serine proteases that activate one another in sequence. The final enzyme in that chain, thrombin, converts a soluble blood protein called fibrinogen into fibrin, which self-assembles into the mesh-like structure of a blood clot. Thrombin also activates platelets, the cell fragments that clump together to seal a wound. Without this protease cascade, even a small cut could lead to dangerous bleeding.
Inside individual cells, a family of proteases called caspases controls programmed cell death, the process your body uses to eliminate damaged, infected, or unnecessary cells. When a cell receives the signal to die, initiator caspases activate executioner caspases, which then systematically cut hundreds of target proteins. This dismantles the cell from the inside in an orderly way, preventing the kind of messy rupture that would trigger inflammation in surrounding tissue. Caspases also participate in non-death cellular remodeling, helping reshape tissues during development.
Plant-Based Proteases
Several well-known proteases come from fruits. Bromelain is a mixture of proteolytic enzymes found primarily in pineapple, papain is a single enzyme extracted from the latex of papaya, and ficin comes from the latex of fig trees. All three belong to the cysteine protease family.
These plant proteases have a long history in food preparation, particularly as meat tenderizers, because they break down the tough connective-tissue proteins in raw meat. Papain is the most commonly used for this purpose. Bromelain is also the reason fresh pineapple can make your mouth feel tingly or sore: it’s literally digesting proteins on the surface of your tongue.
Industrial and Commercial Uses
Proteases are among the most widely used enzymes in industry. In detergent manufacturing, they are not just an additive but a core component of laundry, dishwashing, and industrial cleaning formulas. Alkaline proteases in detergent break down protein-based stains like blood, grass, and food residue. Testing with crude protease extracted from strawberries, for example, showed effective cleaning of ketchup, chocolate sauce, and barbecue sauce stains, illustrating how even novel protease sources can perform well in household products.
Beyond cleaning, proteases are used across the food, pharmaceutical, textile, and leather industries. In cheesemaking, specific proteases curdle milk. In leather production, they help remove hair and soften hides. The commercial enzyme market relies heavily on microbial proteases because bacteria and fungi can be grown at scale to produce large quantities of these enzymes cheaply.
Protease Inhibitors as Medicine
Because many viruses depend on their own proteases to replicate, blocking those enzymes has become a powerful antiviral strategy. HIV protease inhibitors were among the first drugs to turn HIV from a death sentence into a manageable condition. The same principle applies to hepatitis C, where multiple drugs target the virus’s NS3/4A protease, an enzyme the virus needs to process its own proteins and assemble new copies of itself. Several of these drugs gained FDA approval between 2013 and 2017, and they’re now part of combination therapies that can cure hepatitis C in most patients.
Protease Supplements and Inflammation
Oral protease supplements, often labeled as “proteolytic enzymes” or “systemic enzymes,” are marketed for reducing inflammation and speeding recovery from injuries. Clinical research offers some support for these claims. A combination of trypsin and chymotrypsin has been shown to promote healing of traumatic injuries through anti-inflammatory and anti-swelling effects. In patients with rheumatoid arthritis or osteoarthritis, a combination of bromelain, rutin, and trypsin reduced inflammation and pain, while a comparison group taking the standard anti-inflammatory drug diclofenac developed peptic ulcers.
Papain taken orally has been shown to suppress inflammatory signaling pathways involved in skin inflammation resembling atopic dermatitis. Another protease supplement, serrapeptase, demonstrated anti-inflammatory effects comparable to diclofenac in both chronic and acute inflammation models. These findings suggest protease supplements can offer real benefits for certain inflammatory conditions, though results vary depending on the specific enzyme, dose, and condition being treated.