Trypsin chymotrypsins and

Fig. 10.12 Sequence alignment of trypsin, chymotrypsin and thrombin (bovine). The active sites histidine, aspartic acid and serine are highlighted.

The proteolytic enzymes, trypsin, chymotrypsin, and chymoral [8076-22-0] in combination, have been used for the treatment of post-operative hand trauma, athletic injuries, and sciatica (214—216). Trypsin has also been used successfully in treating hyaline membrane disease of newborn babies, a condition usually fatal without treatment (217). Immobilized preparations of trypsin are useful in treating acute radiation cystitis following pelvic x-irradiation therapy (218). 

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. 

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... 

Turnover numbers of enzymes vary from <1 to 106 s . Trypsin, chymotrypsin, and many intracellular... 

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... 

Fig. 14. The rate of hydrolysis of RNase relative to that of Ox-RNase as a function of temperature. The proteases used were (O) aminopeptidase, (A) trypsin, ( ) chymotrypsin, and ( ) carboxypeptidase. Reproduced from Klee (.340).

The proteolytic enzymes trypsin, chymotrypsin, and elas-tase, discussed later on, all work in this way. 

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... 

Hypertensin is soluble in alcohol, glacial acetic acid, phenol, and water, and insoluble in ether (61). Because it is inactivated by tyrosinase it probably contains a catechol or phenol group, and by amine oxidase, an amine group on an a-carbon atom (Figure 2). Hypertensin is inactivated by certain phenolic, catecholic, and amine oxidases, by pepsin, trypsin, chymotrypsin, and carboxypeptidase, and by hypertensinase found in plasma. The nature of hypertensinase is unknown, but it is probably not an oxidative enzyme. Because it is heat-labile, hypertensinase can be removed from blood and renin preparations by heating hypertensin itself is heat-stable. Lack of pure preparations of hypertensin has delayed its further chemical identification. 

Serine proteases. The ft- hydroxy group of serine acts as a nucleophile under slightly alkaline conditions examples are trypsin, chymotrypsin, and subtilisin. 

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. 

The major group of enzymes produced by the pancreas and secreted into the duodenum as an aqueous bicarbonate solution is the peptidases. There are three endopeptidases, trypsin, chymotrypsin and elastase, and two exopeptidases,... 

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