Peptides formation

FIGURE 5.1 Peptide formation is the creation of an amide bond between the carboxyl group of one amino acid and the amino group of another amino acid. Rj and R9 represent the R groups of two different amino acids. 

Suwannachot and Rode (1998) reported an unexpected reaction between peptides and amino acids when using SIPS dialanine formation increased by a factor of 50 in the presence of glycine. The yield depended greatly on the glycine concentration, the optimum value being one eighth of the alanine concentration. Experimental results, as well as calculations, indicate that peptide formation is favoured by an amino acid-monochlorocuprate complex (Fig. 5.6). 

The ribosome is a ribozyme this is how Cech (2000) commented on the report by Nissen et al. (2000) in Science on the successful proof of ribozyme action in the formation of the peptide bond at the ribosome. It has been known for more than 30 years that in the living cell, the peptidyl transferase activity of the ribosome is responsible for the formation of the peptide bond. This process, which takes place at the large ribosome subunit, is the most important reaction of protein biosynthesis. The determination of the molecular mechanism required more than 20 years of intensive work in several research laboratories. The key components in the ribosomes of all life forms on Earth are almost the same. It thus seems justified to assume that protein synthesis in a (still unknown) common ancestor of all living systems was catalysed by a similarly structured unit. For example, in the case of the bacterium E. coli, the two subunits which form the ribosome consist of 3 rRNA strands and 57 polypeptides. Until the beginning of the 1980s it was considered certain that the formation of the peptide bond at the ribozyme could only be carried out by ri-bosomal proteins. However, doubts were expressed soon after the discovery of the ribozymes, and the possibility of the participation of ribozymes in peptide formation was discussed. 

Importantly, it was demonstrated that no significant racemization occurred in the course of peptide formation. Furthermore, the complete coupling of difficult peptide sequences could be accomplished within a few minutes, and it was determined that peptide fragments have higher reactivity than single amino acid derivatives under microwave irradiation conditions. However, the exact reaction temperature during the irradiation period was not determined. 

Bob s research interests and knowledge across chemistry were great. Throughout his career he retained an interest in biomimetic chemistry, specifically the study of metal ion-promoted reactions and reactions of molecules activated by metal ion coordination. His early interests in carbohydrate chemistry inspired him to study metal ion catalysis of both peptide formation and hydrolysis as well as studies in inorganic reaction mechanisms. He was particularly interested in the mechanisms of base-catalyzed hydrolysis within metal complexes and the development of the so-called dissociative conjugate-base (DCB) mechanism for base-catalyzed substitution reactions at inert d6 metal ions such as Co(III). 

All entries of Table 2.1 belong to samples representing the animal kingdom. In order to demonstrate the generality of peptidome concept we analyzed the extract of Avenasativa oat acrospires [34]. Table 2.2 provides the list of peptides found in that plant as well as their tentative protein precursors. Peptide formation in this case seems somewhat less intensive and on the average the peptides are longer than in animal samples. We consider this result as a proof of peptidome formation in plants. Still peptidomics of plants is apparently in its embryonic state and more results are expected in the near future. Procaryotes are not yet studied for generation of peptide pools. 

Gervais, F.G., Xu, D., Robertson, G.S., et al. (1999) Involvement of caspases in proteolytic cleavage of Alzheimer s amyloid-beta precursor protein and amyloidogenic A-beta peptide formation. Cell, 97, 395 06. 

There has been a study of the mechanism of the activation of carboxylic acids to peptide formation by chloro-s -triazines in combination with tertiary amines. The first step, exemplified in Scheme 2 by the reaction of 2-chloro-4,6-disubstituted-l,3,5-triazines (18) with A -methylmorpholine, is formation of a quaternary triazinylammonium salt (20). Here there is NMR evidence for the formation at —50°C of the intermediate (19), showing that the substitution involves the two-step SnAt mechanism rather than a synchronous pathway. The subsequent reaction of (20) with a carboxylic acid yields the 2-acyloxy derivative (21), which carries an excellent leaving group for the amide-forming step. ... 

Peptide Formation of Ribosome (i) amino site Condensation Transfer of amino Release of (i) Formation of... 

H. A. Headlam and P. A. Lay, EPR spectroscopic studies of the reduction of chromium(VI) by methanol in the presence of peptides. Formation of long-lived chromium(V) peptide complexes, Inorg. Chem., 40 (2001) 78-86. 

Different authors used RP-HPLC and UV detection to monitor peptide formation during cheese ripening [174-178], providing valuable information about proteolysis. When large hydrophobic peptide need to be separated an lEC represents the best choice [179]. Nevertheless, the identification of these peptides is essential for the complete understanding of the proteolytic process. The peptides eluted from the LC column can be subjected to ESl-MS for molecular weight determination and MS/MS for amino acid sequence determination, which allow rapid peptide identification [172]. HPLC-ESl-MS and MS/MS techniques have been successfully used for peptide mass fingerprint purposes for sequence analysis of purified albumin from Theobroma cacao seeds [180,181]. 

Effect of milk heating on peptide formation during cheese ripening... 

Characterization of soft cheese proteolysis. Effect of cheese freezing on peptide formation during ripening... 

Chloroquine (Aralen) is one of several 4-aminoquino-line derivatives that display antimalarial activity. Chloroquine is particularly effective against intraerythrocytic forms because it is concentrated within the parasitized erythrocyte. This preferential drug accumulation appears to occur as a result of specific uptake mechanisms in the parasite. Chloroquine appears to work by intercalation with DNA, inhibition of heme polymerase or by interaction with Ca++-calmodulin-mediated mechanisms. It also accumulates in the parasite s food vacuoles, where it inhibits peptide formation and phospholipases, leading to parasite death. 

Krishnan-Ghosh Y, Balasubramanian S (2003) Dynamic covalent chemistry on self-templating peptides formation of a disulfide-linked -hairpin mimic. Angew Chem Int Ed 42 2171-2173... 

Bujdak, J., Slosiarikova, H., Texler, N., Schwendinger, M., and Rode, B. M. (1994). On the possible role of montmorillonites in prebiotic peptide formation. Monats. Chem., 125, 1033-9. 

Rode, B. M., Son, H. L. and Suwannachot, Y. (1999). The combination of salt induced peptide formation reaction and clay catalysis a way to higher peptides under primitive earth conditions. Orig. Life. Evol. Biosph., 29, 273-86. 

During the basic step of peptide formation, two or more reacting components are pre-bonded by the enzyme molecule. A simple model of such reaction can he represented by the diagram in Figure 1.1. 

Excessive heating and excessive evaporation may result in peptide formation. 

Inside the cell, aminoglycosides bind to specific 30S-subunit ribosomal proteins (S12 in the case of streptomycin). Protein synthesis is inhibited by aminoglycosides in at least three ways (Figure 45-3) (1) interference with the initiation complex of peptide formation (2) misreading of mRNA, which causes incorporation of incorrect amino acids into the peptide and results in a nonfunctional or toxic protein and (3) breakup of polysomes into nonfunctional monosomes. These activities occur more or less simultaneously, and the overall effect is irreversible and lethal for the cell. 

Hansen and co-workers have evaluated wheat protein (hard red wheat flour) heated in a model system at various temperatures (108-174 C), moisture levels (13-33%) and times (2-10 minutes) (56,57,58). They found (56) that increasing temperature or time ed to increased peptide formation, and that higher moisture also gave increased peptide formation. 

Active esters peptide synthesis. The reagent in combination with N(C2Hs)j converts N-protected amino acids into active esters (— 85% yield). It can also be used with a tertiary amine to effecl peptide formation between an N-protcctcd amino acid and an amino acid ethyl ester. CBZ-Val-Gly-OC2IIs was prepared in this way in 89% yield. 

Disadvantages of the silver-promoted method for Amdt-Eistert homologation are the large excess of nucleophile required and also the requirement for the use of the free amine during peptide formation procedures. 13 Activation of the diazo ketone by UV light has been shown to be suitable for this type of procedure and good yields are obtained using only 1.2 equivalents of a hydrochloride salt of an amino ester in the presence of triethylamine (Scheme 5). 14 ... 

Solid-Phase Synthesis of (53-Peptides Reaction of Fmoc-Protected Diazo Ketones with Concomitant (53-Peptide Formation on a Solid Support 1401... 

Possibly the most important condensation reaction is that between a carboxylic acid and an amine to give an amide. A great many methods are known by which this formal dehydration process may be carried out, almost all of which involve the two step sequence (i) activation of CO2H COX, where X is a leaving group and (ii) aminolysis of RCOX. Japanese workers have recently advocated the use of 2,2-dichloro-5-(2-phenylethyl)-4-trimethylsilyl-3-furanone (1, "DPTF") for carboxyl activation, and its use for peptide formation is illustrated by the representative conversion 2 —> 3. The byproduct formed from DPTF in these reactions is 5-(2-phenylethyl)-4-trimethylsilylfuran-2,3-dione. 

Small peptides - simple di- and tri-peptides with a primary amine at the N-terminus -catalyse the aqueous aldol between unmodified ketones and aldehydes with up to 86% ee.121 This is dramatically different from the corresponding amino acid-catalysed reaction, suggesting that peptide formation may have been significant in the evolution of asymmetric synthesis. Addition of a-cyclodextrin raised the ee further through the hydrophobic effect. 

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