Chymotrypsin B is one of the digestive enzymes. It is produced by the pancreas and plays an important role in the digestion of proteins.
What is chymotrypsin B?
Chymotrypsin B is a digestive enzyme and belongs to the serine proteases. Serine proteases, in turn, are a subgroup of peptidases. Peptidases are enzymes that can cleave proteins. Serine proteases are characterized by the fact that they carry the amino acid serine in their active center. Other digestive enzymes that belong to the serine proteases are trypsin, elastase and plasmin. Chymotrypsin B is very similar to trypsin in its chemical composition. However, the action of the two digestive enzymes is slightly different.
Function, action, and roles
Chymotrypsin is produced in the pancreas. To prevent the pancreas from digesting itself with this enzyme, it is first formed in the form of the inactive chymotrypsinogen. It is only activated in the small intestine by the chemically similar digestive enzyme trypsin. Trypsin is also released into the small intestine in its inactive form. It is activated there by an enterokinase and can then eventually activate chymotrypsin B. Chymotrypsin B is released into the small intestine along with many other digestive enzymes in the pancreatic secretion. Each day, the pancreas produces about one and a half liters of this secretion. It is strongly alkaline because it is supposed to neutralize the food pulp, which is very acidic after mixing with the gastric juice. The digestive enzymes of the pancreas cannot perform their tasks when the pH is acidic. The secretion of pancreatic juice, and thus the secretion of chymotrypsin B, is stimulated primarily by the hormones cholecystokinin and secretin. Cholecystokinin and secretin are secreted by the cells of the small intestine as soon as they come into contact with acidic food pulp. In contrast, the hormones glucagon, somatostatin, peptide YY, and pancreatic polypeptide inhibit the secretion of pancreatic secretion including its hormones. Also, under the influence of the sympathetic nervous system, less chymotrypsin B is secreted. Chymotrypsin B is excreted in the stool. The values for the digestive enzyme are therefore also measured in the stool. For chymotrypsin in stool, a reference value of > 6 U/g stool applies in adults. The chymotrypsin value provides an indication of the function of the pancreas. An increased excretion of chymotrypsin has no clinical significance. A decreased value may indicate pancreatic dysfunction.
Formation, occurrence, properties, and optimal values
Chymotrypsin B has the task of breaking down proteins in the small intestine. The enzyme works most effectively under alkaline conditions. Protein breakdown already begins by the digestive enzyme pepsin in the stomach. Here, the proteins are broken down into peptides. In the small intestine, protein cleavage is then continued by chymotrypsin B, among others. The protein chains, which have now already been shortened, are broken down by the digestive enzyme into individual amino acids. In this form, the small protein components can be absorbed by the intestinal mucosa and reach the liver via the blood. There they are processed further. Unlike trypsin, chymotrypsin B also has a milk-clotting effect.
Diseases and disorders
A deficiency of chymotrypsin B is usually accompanied by a deficiency of all pancreatic enzymes. This deficiency is usually a consequence of a disorder of the pancreas. This is also referred to as exocrine pancreatic insufficiency (EPI). The disease can have various causes. In children, the most common cause is cystic fibrosis. This is a congenital hereditary disease characterized by viscous secretions in various organs. This includes the pancreas as well as the lungs. In adults, EPI is usually the result of severe pancreatitis. Acute pancreatitis with tissue destruction is usually caused by gallstones or infections with viruses. Chronic pancreatitis usually results from alcohol abuse. However, other genetic or idiopathic diseases can also cause pancreatic insufficiency. As a result, the pancreas can only produce the enzymes or the precursors of the enzymes such as trypsinogen or chymotrypsinogen to a limited extent. If these enzymes are now missing in the digestive tract, the proteins can no longer be broken down and, as a result, can no longer be absorbed by the intestinal mucosa. This digestive disorder is also known as maldigestion.This also puts a strain on the intestinal mucosa. The villi of the intestine atrophy and inflammation occurs. In addition, the intestine is often colonized with harmful bacteria. The disease manifests itself through chronic weight loss. In children, physiological weight gain fails to occur. Even increased food intake cannot stop the weight loss or does not lead to weight gain. The stool of the affected person is rather light in color. It smells bad and is voluminous. In medical terminology, this is referred to as steatorrhea, or fatty stools. Diarrhea can also occur. If too little vitamin K is absorbed via the intestinal mucosa, the result can be an increased tendency to bleed. Normally, if pancreatic insufficiency is suspected, the secretin-pancreozymin test should be used. However, since this is very laborious, the concentration of the enzymes elastase and chymotrypsin in the stool is usually determined via fluorescein dilaurate test. In acute pancreatitis, self-digestion (autodigestion) of the pancreas occurs. Chymotrypsin B is also involved here. Due to obstruction of the pancreatic duct with gallstones, there is a backlog of pancreatic juices and secretions from the small intestine. Small intestinal secretions contain convertase, which activates trypsinogen. Once trypsin is activated, it also activates the other digestive enzymes. Thus, the digestive enzymes begin their work already within the pancreas and break down fats, carbohydrates and proteins. However, it is the fats, carbohydrates and proteins that form the pancreas. Thus, severe inflammation occurs.
