In the small intestine, **peptidases in the brush border membrane (BBM)** (including aminopeptidases, carboxypeptidases, endopeptidases, and dipeptidases) **are responsible for the final stage of peptide digestion** (prior to their absorption into the enterocytes) by reducing most poly- and oligopeptides to their monomer constituents.[4] It is the **pancreatic proteases, trypsin, chymotrypsin, elastase, and carboxypeptidases that continue the digestion process in the intestine**, breaking up large molecules into free amino acids (approximately 30%) and oligopeptides (approximately 70%).[3] These oligopeptides are then further hydrolyzed by brush border and cytosolic peptidases; the paper describes proteolytic activity on dietary peptides, not autolysis of the proteases themselves.

“Proteases constitute a group of enzymes that hydrolyze peptide bonds… Intestinal proteases are an integral part of gut homeostasis and digestion.” It notes that “serine proteases like trypsin and elastases derived from the pancreas play a key role in protein digestion in the upper GI tract,” and that proteolytic activity in the lumen is *tightly regulated* by host protease inhibitors and microbiota so that “proteolytic activity is kept in check.” This shows that pancreatic proteases function in the small intestine as part of a regulated system, rather than simply digesting themselves away.

The paper explains: “After synthesis in the pancreas, these catalytic enzymes are released into the small intestine, where they become activated and are highly effective in digesting ingested food.” It further notes that under pathological conditions, “escape of activated pancreatic enzymes from the intestine into the systemic circulation and tissues” can occur, contributing to organ injury in severe acute pancreatitis. The description emphasizes that, in normal physiology, these enzymes act on food substrates in the intestinal lumen; self‑digestion is discussed mainly in the context of pancreatic and tissue injury, not as a routine fate in the lumen.

Pancreatic juice samples were perfused into the proximal jejunum of human subjects and the concentrations of trypsin and chymotrypsin were measured along the small intestine. The authors reported that the activity of these enzymes decreased progressively along the small intestine. They attributed the fall in activity largely to proteolytic destruction (autodigestion and digestion by other proteases) and to adsorption onto particulate matter, rather than to absorption as intact enzymes into the bloodstream.

This chapter describes **intestinal brush border peptidases (aminopeptidases A and N and dipeptidyl peptidase IV)** and their roles in digestion and absorption. It notes that **“the number of peptidases found in enterocytes in the small intestine is large, because of the large number of different peptide bonds in oligopeptides produced by the action of pancreatic proteases.”** The emphasis is on brush-border and enterocyte enzymes acting on peptide substrates generated by pancreatic proteases, rather than on the proteases digesting themselves into amino acids as they move distally.

Salk scientists describe how pancreatic enzymes can be dangerous if activated in the wrong place: “Every day, your pancreas produces about one cup of digestive juices, a mixture of molecules that can break down the food you eat. But if these powerful molecules become activated before they make their way to the gut, they can damage the pancreas itself—digesting the very cells that created them, leading to the painful inflammation known as pancreatitis.” They identify estrogen‑related receptor gamma (ERRγ) as “critical for preventing pancreatic auto‑digestion,” showing that self‑digestion is a pathological risk *inside the pancreas* when activation is premature, not the normal outcome once enzymes are in the intestinal lumen.

This study measured the fate of pancreatic enzymes in the human small intestine and reported that **pancreatic enzymes undergo luminal degradation as they pass along the intestine**. It found that **enzyme activities and concentrations decrease from proximal to distal segments**, consistent with proteolytic breakdown and dilution. However, the paper treats this as a factor limiting digestive efficiency and enzyme replacement therapy, not as a designed mechanism to digest the enzymes themselves into amino acids for absorption.

This chapter notes that in the small intestine, pancreatic enzymes such as trypsin and chymotrypsin continue digestion, producing tripeptides, dipeptides, and free amino acids. It explains that most digestion and absorption occur in the small intestine as pancreatic enzymes and bile break food into its simplest components so that they can enter the body. It also describes that monosaccharides, amino acids, and lipid components are absorbed across the intestinal lining, implying that proteins and peptides are ultimately reduced to amino acids and small peptides close to the mucosal surface.

Total protein entering the gut lumen each day includes 70–100 g of dietary protein and about 35–200 g of endogenous protein (enzymes, mucus, desquamated cells). All of these proteins are substrates for proteolysis in the intestinal lumen and at the brush border. Ultimately, they are hydrolyzed to amino acids and small peptides, which are absorbed by the small intestine, so that very little protein normally reaches the colon.

The review notes: “All **pancreatic proteases are secreted as inactive zymogens to prevent the pancreas from digesting itself**.” It then describes the activation cascade in the duodenum: “The cascade works like a row of dominoes: enteropeptidase activates trypsinogen into trypsin; trypsin then activates other pancreatic zymogens.” The text emphasizes prevention of auto‑digestion within the pancreas and the role of activation in the intestinal lumen, but does not state that the enzymes normally digest themselves into amino acids; rather, they catalyze digestion of dietary proteins until inactivated or degraded.

In describing protein digestion, Khan Academy states that **brush border peptidases break peptide bonds on the enterocyte surface**, and that the pancreas adds trypsinogen and chymotrypsinogen, which are activated (via enteropeptidase) to trypsin and chymotrypsin to **break down peptide bonds in luminal proteins and polypeptides**. The video clarifies that **large proteins cannot be absorbed, so they are broken into amino acids and small peptides**, with the final steps occurring at the brush border and inside enterocytes. It does not describe a physiological process where active proteases in the distal small intestine predominantly digest themselves or other enzymes into amino acids.

This physiology lecture explains that pancreatic proteases like trypsin, chymotrypsin, and carboxypeptidases are secreted as zymogens and activated in the duodenum, where they break dietary proteins into smaller peptides. It further notes that many brush‑border enzymes of the small intestine “are attached to the membrane of the cells and can digest disaccharides and dipeptides directly on the membrane,” describing how final digestion to amino acids occurs at the mucosal surface. The focus is on substrate proteins and peptides; the lecture does not describe proteases digesting themselves as the primary route of their breakdown.

A lay explanation of trypsin states: “Because if the pancreas produced active trypsin, the enzyme would start **digesting the pancreas itself**! Once it reaches the small intestine, it's activated and can then break down protein into smaller peptides and amino acids.” This piece underscores that the main concern about self‑digestion is within the pancreas before secretion, and that after activation in the intestine the enzyme’s physiological role is to digest dietary protein, not to digest itself.

Standard physiology texts describe that pancreatic proteases (e.g., trypsin, chymotrypsin, elastase) are active in the duodenal and jejunal lumen for a limited time, where they cleave dietary proteins and also can cleave one another’s peptide bonds. Over time they are inactivated by dilution, pH changes, binding to inhibitors (such as pancreatic secretory trypsin inhibitor and other protease inhibitors in the lumen), and nonspecific proteolysis. A small fraction of intact enzymes or fragments may be degraded further by other proteases, but these enzymes are not a major nutritional protein source; most amino acids absorbed in the small intestine derive from dietary and endogenous mucosal proteins rather than from complete self‑digestion of the proteases themselves.

This explanatory article describes that proteases in the small intestine cut proteins into smaller chains, and brush border enzymes then "snip the final bonds of small peptides to release individual amino acids that can pass through the intestinal wall and into your bloodstream." It notes that digestive enzymes are specialized proteins that work on food but do not themselves enter the bloodstream intact; instead, they remain in the lumen and are eventually broken down.

The article explains that dietary protein entering the body is digested by gastric pepsin, pancreatic proteases (trypsin, chymotrypsin, carboxypeptidase) and intestinal enzymes such as aminopeptidase and dipeptidase, ultimately becoming amino acids. It notes that in the small intestine, digestion of protein occurs at the microvillus membrane of epithelial cells and that amino acids produced are immediately absorbed through transport proteins in the brush border, leaving little intact protein in the distal small intestine.

The piece explains that proteases are released by the pancreas into the proximal small intestine, where they mix with proteins denatured by gastric secretions and break them down into amino acids, the building blocks of protein, which are then absorbed and used throughout the body. It underscores that the purpose of proteases is to act on dietary proteins rather than to be absorbed intact, and that as proteins themselves, digestive enzymes will also be subject to breakdown.