Chymotrypsin, peptide cleavage with

Chrysanthemic acid, structure of, 107 Chymotrypsin, peptide cleavage with, 1033... 

This clever strategy is illustrated in Scheme 10.5. Selective cleavage of short N -protected peptide substrates with chymotrypsin from the surface area of TentaGel-... 

Exercise 25-30 The proteolytic enzyme, papain, differs from chymotrypsin in having cysteine, or a labile derivative thereof, as part of its active site. The enzyme is deactivated by substances that form complexes with, or react with, —SH groups and the activity is restored by reactions expected to regenerate an —SH group. Work out a schematic mechanism for cleavage of a peptide chain with papain that involves acylation of the critical —SH group of papain. 

From a rare fungus you have isolated an octapeptide that prevents baldness, and you wish to determine the peptide sequence. The amino acid composition is Lys(2), Asp, Tyr, Phe, Gly, Ser, Ala. Reaction of the intact peptide with FDNB yields DNP-alanine plus 2 moles of e-DNP-lysine on acid hydrolysis. Cleavage with trypsin yields peptides the compositions of which are (Lys, Ala, Ser) and (Gly, Phe, Lys), plus a dipeptide. Reaction with chymotrypsin releases free aspartic acid, a tetrapeptide with the composition (Lys, Ser, Phe, Ala), and a tripeptide the composition of which, following acid hydrolysis, is (Gly, Lys, Tyr). What is the sequence ... 

Dynorphin (D)is a neuropeptide. Indicate the -terminal end and the C-terminal end. Show the products of cleavage with (a) trypsin (b) chymotrypsin. Show the A-phenylthiohydantoin that results from treatment of D with phenyl isothiocyanate. Do you expect D to be an acidic, a neutral or a basic peptide ... 

The fragmentation of a larger peptide is acheived by chemical cleavage with cyanogen bromide or enzymatically by endopeptidase, such as trypsin or chymotrypsin. 

Barany et al. were the first to exploit the different enzyme accessibilities of surface and interior areas of a given bead and the resulting differentiated bead was used to synthesize a peptide library on the surface and the code for this on the interior simultaneously 307. This clever strategy is illustrated in Fig. 18-31. Selective cleavage of short N°-protected peptide substrates with chymotrypsin from the surface area of... 

Most polypeptides in nature are longer than 20 to 30 amino acids, the practical limit on the number of amino acids that can be sequenced by repetitive Edman degradation. The special value of cleavage with cyanogen bromide, trypsin, and chymotrypsin is that, at specific peptide bonds, a long polypeptide chain can be cleaved into smaller polypeptide fragments, and each fragment can then be sequenced separately. 

Consider the structure of the following cyclic octapeptide. Would cleavage of this peptide with trypsin produce different fragments than cleavage with chymotrypsin Explain. 

Selective cleavage of a peptide occurs with trypsin and chymotrypsin to identify the location of specific amino acids (Table 28.2). 

With some enzymes, the cleavage of one or more internal peptide bonds does not cause protein disruption and can in fact lead to an increase in enzyme activity. This occurs not only during the processing of proenzymes, such as the conversion of trypsinogen to trypsin or chy-motrypsinogen to chymotrypsin, but also with intracellular enzymes such as hepatic fructose bisphosphatase (Pontremoli et al., 1973). This enzyme does not fall apart upon limited proteolytic cleavage, because... 

The porcine insulin is first subjected to digestion with chymotrypsin-free trypsin at pH 7.5 for in excess of 45 min. This results in the selective cleavage of the peptide bond linking arginine 22... 

Bovine pancreatic chymotrypsin (Mr 25,191) is a protease, an enzyme that catalyzes the hydrolytic cleavage of peptide bonds. This protease is specific for peptide bonds adjacent to aromatic amino acid residues (Trp, Phe, Tyr). The three-dimensional structure of chymotrypsin is shown in Figure 6-18, with functional groups in the active site emphasized. The reaction catalyzed by this enzyme illustrates the principle of transition-state stabilization and also provides a classic example of general acid-base catalysis and covalent catalysis. 

MECHANISM FIGURE 6-21 Hydrolytic cleavage of a peptide bond by chymotrypsin. The reaction has two phases. In the acylation phase (steps to ), formation of a covalent acyl-enzyme intermediate is coupled to cleavage of the peptide bond. In the deacylation phase (steps to ), deacylation regenerates the free enzyme this is essentially the reverse of the acylation phase, with water mirroring, in reverse, the role of the amine component of the substrate. Chymotrypsin Mechanism... 

The inactive precursors are called trypsinogen, pepsinogen, chymotrypsino-gen, and procarboxypeptidase. These precursors are converted to the active enzymes by hydrolytic cleavage of a few specific peptide bonds under the influence of other enzymes (trypsin, for example, converts chymotrypsinogen to chymotrypsin). The digestive enzymes do not appear to self-destruct, probably because they are so constructed that it is sterically impossible to fit a part of one enzyme molecule into the active site of another. In this connection, it is significant that chymotrypsin attacks denatured proteins more rapidly than natural proteins with their compact structures of precisely folded chains. 

The stereochemical aspects of peptide hydrolysis catalyzed by chymotrypsin and related serine proteases has been recently analyzed with respect to requirements for stereoelectronic control of bond cleavage and this analysis has led to a much more complete understanding of the reaction mechanism (9-14). 

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