Peptides cleavage, selective

Cyclotriboroxanes as intermediates 27,158 Cysteine peptides, cleavage, selective 20, 37 suppl. 27... 

In Sect. 6.4.1, the metabolic fate of a few peptides in selected tissues was summarized, pointing to the involvement of classes of peptidases. Here, we consider a number of important bioactive peptides (taken in alphabetical order) and examine the qualitative aspect of their cleavage by purified peptidases. The symmetrical viewpoint, namely the activity of peptidases toward various peptides, is presented in Table 6.6. 

The best way to show you t>ow the overlap method of peptide sequencing works is by a specific example. In this example, we will illustrate the use of the two most commonly used enzymes for selective peptide cleavage. One is trypsin, a proteolytic enzyme of the pancreas (MW 24,000) that selectively catalyzes the hydrolysis of the peptide bonds of basic amino acids, lysine and... 

Know the meaning of amino acid sequence, Sanger s reagent, Edman degradation, selective peptide cleavage. 

Given information on selective peptide cleavage and the sequences of fragment peptides, deduce the sequence of the original polypeptide. 

Proteins are typically made as pro-proteins and are then subsequently modified by post-translational processing involving selective proteolysis ( trimming ) and addition of other groups. Thus, nascent polypeptides commence with N-formylmethionine (bacteria) or methionine (eukaryotes). However, N-terminal sequences are often removed in proteolytic processing. In many eukaryote proteins, the final N-terminal amino acid of the processed protein is N-acetylated. The C-terminus may also be changed by peptide cleavage and other covalent modification. 

This chapter is a preview rather than a review. Most of the selective chemical methods for peptide cleavage have been thought about or tested only very recently. Although these methods have been applied to simple peptide models, only a few field studies with enzymes and proteins have been pursued. However, these chemical methods introduce a new challenging approach which may make possible structural work on more complex proteins with large molecular weights. 

The criteria for a useful selective peptide cleavage, applicable to the study of sensitive enzymes without causing side effects or denaturation, are (a) the reagent must react with only one reactive site (6) the rate of reaction should be rapid (c) addition of the reagent to the reactive site should yield a highly unstable intermediate (d) the great instability... 

Another possible aspect of histidine peptide cleavage is introduced by the great lability of 4(5H)-imidazolones (CXXXIII) (Freter el al., 19.57 Brown and Kies, 1959). In their lability and eagerness to open up to forma-raidino acids (CXXXIV) they almost resemble anhydrides (Kny and Witkop, 1959). It is not unlikely that such 4(5H)-imidazolones can be produced nonenzymatically. Such selective oxidation of a histidine peptide to a 4(5H)-imidazolone derivative introduces the possibility of translacta-... 

The multiple number of the interactions between CF and peptide deformylase suggested by the simulations experiments accounts for the high selectivity manifested by CF and peptide deformylase. When tested with 15 other proteins, CF did not cleave the proteins. The organic moiety of CF selected from the chemical library containing 15,000 compounds forms a productive complex with peptide deformylase. The Co(III) center of CF appears to be located in a highly productive position in the peptide deformylase-catalyst complex. The high effective molarity of the Co(III) center thus achieved apparently led to effective peptide cleavage. 

Cleavage of proteins at methionine with cyanogen bromide yields peptides that have homoserine at the COOH-terminus. Treatment of the peptide with anhydrous trifluoroacetic acid results in a lactone that is sufficiently activated to undergo aminolysis by aliphatic amines (Horn, 1975) or sequencing resins (Wachter et ai, 1975 Horn and Laursen, 1973 Bridgen, 1975) (Fig. 5). In this way, peptides are selectively attached at the COOH-terminus without the need for amino or carboxyl protection. Resins incorporating a )5-diamine structure, such as triethylenetetramine (TETA) polystyrene (Horn and Laursen, 1973) and j8-aminoethylaminopropylglass... 

The concept of naked anions, i.e. anions solubilized in non-solvating media by the crown complexation of their counter-cations, has been applied further this year. Naked fluoride ion has been used as a catalyst for Michael additions,such as the cyanoethylation of active methylene compounds, and also as a base to mediate the acylation (and protection) of the indole nitrogen of tryptophan in peptides. The selective cleavage of protected amino-acids from oxyacyl resins [equation (18)] is a... 

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