Trypsin, hydrolysis catalyzed

Trypsin (Section 27 10) A digestive enzyme that catalyzes the hydrolysis of proteins Trypsin selectively catalyzes the cleavage of the peptide bond between the carboxyl group of lysine or arginine and some other amino acid... 

Latent forms of a neutral protease and an acid protease (pH optimum 5.3) from cartilage are activated by trypsin hydrolysis to give Ca2+-dependent enzymes that catalyze the hydrolysis of proteoglycan.406 Some Ca2+-dependent proteinases are isolated as proenzymes that can be converted to the active form by high [Ca2+] or by low [Ca2+] in the presence of a digestable substrate.407... 

Considerable effort has been applied to studies of ester hydrolysis catalyzed by imidazoles (76MI40700, 80AHC(27)241). Certainly, 1-acetylimidazole can be made enzymically, probably by the sequence acetyl phosphate + coenzyme A acetylcoenzyme A+phosphate, acetyl-coenzyme A + imidazole l-acetylimidazole+coenzyme A. In addition, the imidazolyl group of histidine appears to be implicated in the mode of action of such hydrolytic enzymes as trypsin and chymotrypsin, thereby engendering further interest in the process of imidazole catalysis. The two pathways which have been found to be involved are general base catalysis and nucleophilic catalysis. In the former (Scheme 26) a basic imidazole molecule can activate a water molecule to attack the ester at the carbonyl carbon, this being followed by the usual sequence of steps as in simple hydroxide ion hydrolysis. At high imidazole concentrations the imidazole molecules may be involved directly. 

Fio. 7. Stepwise formation of the three chains of a-chymotrypsin (A ) (64). ChTg, bovine chymotrypsinogen A. ChT-jr, -i and -a, respectively, ir-chymotrypsin (Ai), S-chymotrypsin (Aj), and -chymotrypsin (Ad. Neo-ChTg, neochymotrypsinogens (degraded and still activatable forms of chymotrypsinogen A). + and —, NHs- and COOH-terminal residues, respectively. T.C. and C.C., hydrolysis catalyzed by trypsin and chymotrypsin, respectively. Asp, asparagine residue. A, B, and C, chains A, B, and C of a-chymotrypsin (Ad. 

Latent forms of a neutral protease and an acid protease (pH optimum 5.3) from cartilage are activated by trypsin hydrolysis to give Ca -dependent enzymes that catalyze the hydrolysis of... 

Thus, trypsin will catalyze the hydrolysis of three peptide bonds in the following peptide, creating a hexapeptide, a dipeptide, and two tripeptides. 

Site-specific cleavs (Section 24.5D) A method of cleaving peptides at specific, known sites using enzymes and specialized reagents. For example, the enzyme trypsin preferentially catalyzes hydrolysis of peptide bonds on the C-terminal side of arginine and lysine. Other bonds in the peptide are not cleaved by this reagent. 

The peptide shown m green was isolated by trypsin catalyzed hydrolysis and has an ammo acid sequence that completes the remaining overlaps... 

Partial hydrolysis of a peptide can be carried out either chemically with aqueous acid or enzymatically. Acidic hydrolysis is unselective and leads to a more or less random mixture of small fragments, but enzymatic hydrolysis is quite specific. The enzyme trypsin, for instance, catalyzes hydrolysis of peptides only at the carboxyl side of the basic amino acids arginine and lysine chymotrypsin cleaves only at the carboxyl side of the aryl-substituted amino acids phenylalanine, tyrosine, and tryptophan. 

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. 

Procarboxypeptidase A is activated by the removal of a peptide of some 64 residues from the N-terminus by trypsin.153 This zymogen has significant catalytic activity. As well as catalyzing the hydrolysis of small esters and peptides, procarboxypeptidase removes the C-terminal leucine from lysozyme only seven times more slowly than does carboxypeptidase. Also, the zymogen hydrolyzes Bz-Gly-L-Phe with kcsA = 3 s-1 and KM = 2.7 mM, compared with values of 120 s 1 and 1.9 mM for the reaction of the enzyme.154 In contrast to the situation in chymotrypsinogen, the binding site clearly pre-exists in procarboxypeptidase, and the catalytic apparatus must be nearly complete. 

Wang, S.S., and Carpenter, F.H. (1968) Kinetic studies at high pH of the trypsin-catalyzed hydrolysis of Na-benzoyl derivatives of L-arginamide, L-lysinamide, and S-2-aminoethyl-L-cysteinamide and related compounds./. Biol. Chem. 243, 3702-3710. 

Fig. 3.3. Major steps in the hydrolase-catalyzed hydrolysis of peptide bonds, taking chymo-trypsin, a serine hydrolase, as the example. Asp102, His57, and Ser195 represent the catalytic triad the NH groups of Ser195 and Gly193 form the oxyanion hole . Steps a-c acylation Steps d-f deacylation. A possible mechanism for peptide bond synthesis by peptidases is represented by the reverse sequence Steps f-a.

This enzyme [EC 3.4.21.10] catalyzes the hydrolysis of Arg-Xaa and Lys-Xaa peptide bonds. The enzyme belongs to the peptidase family SI and is inhibited by naturally occurring trypsin inhibitors. 

Thrombin [EC 3.4.21.5], also known as fibrinogenase, catalyzes the hydrolysis of peptide bonds, exhibiting preferential cleavage for the Arg—Gly peptide bond. The enzyme, a member of the peptidase family SI, activates fibrinogen to fibrin and releases fibrinopeptide A and B. Thrombin, formed from prothrombin, is more selective in peptide hydrolysis than trypsin or plasmin. 

On-line hydrolysis of proteins catalyzed by trypsin or pepsin immobilized on monolithic silica beds was described by Kato et al. [86,195], whereas pepsin was encapsnlated into the silica-gel matrix (75 pm capillary column), without loss in enzymatic activity [195]. 

Among proteases, the digestive enzyme trypsin catalyzes the hydrolysis of only those peptide bonds in which the carbonyl group is contributed by either a Lys or an Arg residue, regardless of the length or amino acid sequence of the chain. The number of smaller peptides produced by trypsin cleavage can thus be predicted... 

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