Proteases are enzymes that facilitate chemical reactions. Their primary function is to break down other proteins, a process known as proteolysis, by hydrolyzing the peptide bonds that link amino acids. Often called “molecular scissors,” they cut long proteins into smaller pieces or individual amino acids. This process occurs in all forms of life, from bacteria to animals.
Biological Roles of Proteases
The function of proteases extends throughout the body. One of their most recognized roles is in digestion. In the stomach, pepsin begins breaking down proteins from food, and the process continues in the small intestine with proteases like trypsin and chymotrypsin. These enzymes dismantle protein chains into amino acids that can be absorbed and used by the body.
Proteases are also integral to the immune system, helping to activate immune responses and destroy pathogens. Another function is in blood clotting. When a blood vessel is injured, a series of proteases activate each other in a sequence called the clotting cascade, forming a stable clot that prevents excessive bleeding.
Within individual cells, proteases perform housekeeping duties. They are responsible for protein catabolism, the breakdown and recycling of old or damaged proteins. This process maintains cellular components and prevents the accumulation of potentially harmful protein aggregates.
Regulation and Control of Protease Activity
Given their ability to break down proteins, protease activity must be tightly controlled to prevent tissue damage. One regulatory mechanism is producing them in an inactive form called a zymogen. For example, the digestive enzyme pepsin is produced as pepsinogen and is only activated in the acidic environment of the stomach where it is needed.
This ensures the protease remains inert until it reaches its target location. Another layer of control is provided by protease inhibitors. These molecules bind to active proteases and block their function, acting as a natural “off switch” to ensure proteolysis only occurs when and where required.
Consequences of Protease Imbalance
When the balance between proteases and their inhibitors is disrupted, it can lead to various diseases. Uncontrolled protease activity is a factor in inflammatory conditions like emphysema, where an excess of proteases destroys elastic fibers in the lungs. This imbalance is often linked to factors that reduce the effectiveness of protease inhibitors.
Proteases also have a role in the progression of cancer. Some tumors use proteases to degrade the extracellular matrix, the network of proteins surrounding cells. This breakdown allows the tumor to invade nearby areas and metastasize, or spread, to other parts of the body.
Protease activity is also relevant in viral infections. The human immunodeficiency virus (HIV), for instance, relies on its own protease to replicate and assemble new, infectious particles. Because this viral protease is distinct from human proteases, it has become a target for antiviral medications.
Proteases in Commercial and Medical Use
Humans have harnessed proteases for a wide range of practical purposes. In the food industry, they are used as meat tenderizers. Enzymes like papain from papaya and bromelain from pineapple break down tough connective tissues in meat. Rennet, a complex of enzymes containing the protease chymosin, is used in cheesemaking to hydrolyze milk proteins and form curds.
Consumer products also contain proteases. They are an ingredient in laundry and dish detergents, where they break down protein-based stains such as blood, grass, and food residue. This enzymatic action allows for effective cleaning at lower temperatures.
In the medical field, proteases are used in wound debridement to clean away damaged tissue and promote healing. Targeting proteases is also a therapeutic strategy. Protease inhibitor drugs are used to treat viral infections like HIV and Hepatitis C by blocking the viral proteases necessary for replication.