Trypsin elastase and

Proteinases and antiproteinases are part of the normal protective and repair mechanisms in the lungs. The imbalance of proteinase-antiproteinase activity in COPD is a result of either increased production or activity of destructive proteinases or inactivation or reduced production of protective antiproteinases. AAT (an antiproteinase) inhibits trypsin, elastase, and several other proteolytic enzymes. Deficiency of AAT results in unopposed proteinase activity, which promotes destruction of alveolar walls and lung parenchyma, leading to emphysema. 

Trypsin, elastase, and chymotrypsin are endopeptida-ses. Carboxypeptidases are exopeptidases (Table 12-5). The combined action of these enzymes produces oligopeptides having two to six amino acid residues and free... 

Much but not all of this work has dealt with proteins the three-dimensional structures of which have been determined by x ray lysozyme, ribonuclease, myoglobin, hemoglobin, cytochrome C, carboxy-peptidase, chymotrypsin, concanavalin, trypsin, elastase, and sub-tilisin. The principal nucleus has been the proton, but more recently 13 C has been studied by several groups. Other nuclei, such as 19 F, 31P, and 35Cl, have found limited application in special studies. 

The specificity of compound 1 for AChE was demonstrated by treating other proteases of the His-Ser-Asp charge relay mechanism with the potential inhibitor. Trypsin, elastase, and subtilisin were not inactivated by 1. Chymotrypsin and kallikrein showed barely detectable inactivation at 100 IM and 40-45% inactivation at 1 mM. Conpounds 2, 3, and 5 also inactivated the eel AChE. Compound 2 showed 95% inactivation at 100 IM in 15 min. Conpounds 3 and 5 showed IC50 values of 102 XM and 108 1M, respectively. 

Trypsin, chymotrypsin, and elastase all carry out the same reaction—the cleavage of a peptide chain—and although their structures and mechanisms are quite similar, they display very different specificities. Trypsin cleaves peptides... 

FIGURE 16.19 The substrate-binding pockets of trypsin, chymotrypsin, and elastase. 

There are two main classes of proteolytic digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolyzed. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. They are the first enzymes to act, yielding a larger number of smaller fragments, eg, pepsin in the gastric juice and trypsin, chymotrypsin, and elastase secreted into the small intestine by the pancreas. Exopeptidases catalyze the hydrolysis of peptide bonds, one at a time, fi"om the ends of polypeptides. Carboxypeptidases, secreted in the pancreatic juice, release amino acids from rhe free carboxyl terminal, and aminopeptidases, secreted by the intestinal mucosal cells, release amino acids from the amino terminal. Dipeptides, which are not substrates for exopeptidases, are hydrolyzed in the brush border of intestinal mucosal cells by dipeptidases. 

Irreversible inhibition is probably due to the alkylation of a histidine residue.43 Chymotrypsin is selectively inactivated with no or poor inhibition of human leukocyte elastase (HLE) with a major difference the inactivation of HLE is transient.42,43 The calculated intrinsic reactivity of the coumarin derivatives, using a model of a nucleophilic reaction between the ligand and the methanol-water pair, indicates that the inhibitor potency cannot be explained solely by differences in the reactivity of the lactonic carbonyl group toward the nucleophilic attack 43 Studies on pyridyl esters of 6-(chloromethyl)-2-oxo-2//-1 -benzopyran-3-carboxylic acid (5 and 6, Fig. 11.5) and related structures having various substituents at the 6-position (7, Fig. 11.5) revealed that compounds 5 and 6 are powerful inhibitors of human leukocyte elastase and a-chymotrypsin thrombin is inhibited in some cases whereas trypsin is not inhibited.21... 

A large group of proteinases contain serine in their active center. The serine proteases include, for example, the digestive enzymes trypsin, chymotrypsin, and elastase (see pp. 94 and 268), many coagulation factors (see p. 290), and the fibrinolytic enzyme plos-min and its activators (see p. 292). 

Trypsin, chymotrypsin, and elastase are en-dopeptidases that belong to the group of serine proteinases (see p. 176). Trypsin hydrolyzes specific peptide bonds on the C side of the basic amino acids Arg and Lys, while chymotrypsin prefers peptide bonds of the apolar amino acids Tyr, Trp, Phe, and Leu (see p. 94). 

Protein degradation is initiated by proteinoses—hy pepsins in the stomach and by trypsin, chymotrypsin, and elastase in the small intestine. The resulting peptides are then further hydrolyzed by various peptidases into amino... 

In the small intestine, proteases released by the pancreas as zymogens become active. Each has a different specificity for the amino acid R-groups adjacent to the susceptible peptide bond. Examples of these enzymes are trypsin, chymotrypsin, elastase, and car-boxypeptidase A and B. The resulting oligopeptides are cleaved by aminopeptidase found on the luminal surface of the intestine. Free amino acids and dipeptides are then absorbed by the intestinal epithelial cells. 

The digestive enzymes trypsin, chymotrypsin, elastase, and proteinase E are related serine proteases. All three are synthesized in the pancreas which secretes 5-10 g per day of proteins, mostly the inactive proenzymes (zymogens) of digestive enzymes.191,192... 

From study of peptides formed by partial hydrolysis of the 32P-labeled chymotrypsin, the sequence of amino acids surrounding the reactive serine was established and serine 195 was identified as the residue whose side chain hydroxyl group became phosphorylated. The same sequence Gly-Asp-Ser-Gly was soon discovered around reactive serine residues in trypsin, thrombin, elastase, and in the trypsin-like cocoonase used by silkmoths to escape from their cocoons.198 We know now that these are only a few of the enzymes in a very large family of serine proteases, most of which have related active site sequences.199 200 Among these are thrombin and other enzymes of the blood-clotting cascade (Fig. 12-17), proteases of lysosomes, and secreted proteases. 

The mammalian serine proteases have a common tertiary structure as well as a common function. The enzymes are so called because they have a uniquely reactive serine residue that reacts irreversibly with organophosphates such as diisopropyl fluorophosphate. The major pancreatic enzymes—trypsin, chymotrypsin, and elastase—are kinetically very similar, catalyzing the hydrolysis of peptides... 

The serine proteases are a large family of proteolytic ( enzymes that use the reaction mechanism for nucleophilic catalysis outlined in equations (3) and (4), with a serine residue as the reactive nucleophile. The best known members of the family are three closely related digestive enzymes trypsin, chymotrypsin, and elastase. These enzymes are synthesized in the mammalian pancreas as inactive precursors termed zymogens. They are secreted into the small intestine, where they are activated by proteolytic cleavage in a manner discussed in chapter 9. 

In the digestive system trypsin, chymotrypsin, and elastase work as a team. They are all endopeptidases, which means that they cleave protein chains at internal peptide bonds, but each preferentially hydrolyses bonds adjacent to a particular type of amino acid residue (fig. 8.4). Trypsin cuts just next to basic residues (lysine or arginine) chymotrypsin cuts next to aromatic residues (phenylalanine, tyrosine, or tryptophan) elastase is less discriminating but prefers small, hydrophobic residues such as alanine. 

Trypsin, chymotrypsin, and elastase—three members of the serine protease family—catalyze the hydrolysis of proteins at internal peptide bonds adjacent to different types of amino acids. Trypsin prefers lysine or arginine residues chymotrypsin, aromatic side chains and elastase, small, nonpolar residues. Carboxypeptidases A and B, which are not serine proteases, cut the peptide bond at the carboxyl-terminal end of the chain. Carboxypeptidase A preferentially removes aromatic residues carboxypeptidase B, basic residues. (Illustration copyright by Irving Geis. Reprinted by permission.)... 

In chapter 8, we mentioned that the pancreas secretes trypsin, chymotrypsin, and elastase as inactive zymogens, which are activated by extracellular proteases. Trypsin is activated when the intestinal enzyme enter-opeptidase cuts off an N-terminal hexapeptide. Trypsin in turn activates chymotrypsin by cutting it at the N-terminal end between Arg 15 and lie 16. This type of change in the covalent structure of an enzyme is termed partial proteoly-sis. Delaying the activation prevents the digestive enzymes from destroying the pancreatic cells in which they are synthesized. 

For instance, the mammalian serine proteases — trypsin, chymotrypsin, and elastase—are very similar in structure and conformation. If a new mammalian serine protease is discovered, and sequence homology with known proteases... 

Aprotinin is a polypeptide consisting of 58 amino acid residues derived from bovine lung tissues and shows inhibitory activity toward various proteolytic enzymes including chymo-trypsin, kallikrein, plasmin, and trypsin. It was also one of the first enzyme inhibitors used as an auxiliary agent for oral (poly)peptide administration. The co-administration of aprotinin led to an increased bioavailability of peptide and protein drugs [5,44,45], The Bowman-Birk inhibitor (71 amino acids, 8 kDa) and the Kunitz trypsin inhibitor (184 amino acids, 21 kDa) belong to the soybean trypsin inhibitors. Both are known to inhibit trypsin, chymotrypsin, and elastase, whereas carboxypeptidase A and B cannot be inhibited [7,46],... 

The substrate specificity of an enzyme is determined by the properties and spatial arrangement of the amino acid residues forming the active site. The serine proteases trypsin, chymotrypsin and elastase cleave peptide bonds in protein substrates on the carboxyl side of positively charged, aromatic and small side-chain amino acid residues, respectively, due to complementary residues in their active sites. 

The properties and spatial arrangement of the amino acid residues forming the active site of an enzyme will determine which molecules can bind and be substrates for that enzyme. Substrate specificity is often determined by changes in relatively few amino acids in the active site. This is clearly seen in the three digestive enzymes trypsin, chymotrypsin and elastase (see Topic C5). These three enzymes belong to a family of enzymes called the serine proteases - serine because they have a serine residue in the active site that is critically involved in catalysis and proteases because they catalyze the hydrolysis of peptide bonds in proteins. The three enzymes cleave peptide bonds in protein substrates on the carboxyl side of certain amino acid residues. 

Trypsin, chymotrypsin, and elastase are three of the most important protein-digesting enzymes secreted by the pancreas. Despite their similarities they have different substrate specificity, that is, they cleave different peptide bonds during protein digestion. 

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