Peptides tripeptides

RGD peptides Tripeptide sequencer close to caspase-3 active site Disrupts intramolecular interaction resulting in caspase-3 activation Clinical use as antithorobic agent Potenteial use as anti-angiogenic agent 98... 

Entry UNCA Amino Ester Di peptide/ Tripeptide Conversion (%) Yieid (%) ... 

There are several levels of pepfide sfrucfure The primary structure is the ammo acid sequence plus any disulfide links With the 20 ammo acids of Table 27 1 as building blocks 20 dipeptides 20 tripeptides 20" tetrapeptides and so on are possible Given a peptide of unknown structure how do we determine its ammo acid sequence" ... 

Tripeptide (Section 27 1) A compound m which three a ammo acids are linked by peptide bonds... 

The sequence of amino acids in a peptide can be written using the three-letter code shown in Figure 45.3 or a one-letter code, both in common use. For example, the tripeptide, ala.ala.phe, could be abbreviated further to AAF Although peptides and proteins have chain-like structures, they seldom produce a simple linear system rather, the chains fold and wrap around each other to give complex shapes. The chemical nature of the various amino acid side groups dictates the way in which the chains fold to arrive at a thermodynamically most-favored state. 

A dipeptide is a molecule consisting of two anino acids joined by a peptide bond. A tripeptide has three amino acids joined by two peptide bonds, a tetrapeptide has four fflnino acids, and so on. Peptides with more than 30-50 anino acids are polypeptides. Proteins are polypeptides that have some biological function. 

Peptide is the name assigned to short polymers of amino acids. Peptides are classified by the number of amino acid units in the chain. Each unit is called an amino acid residue, the word residue denoting what is left after the release of HgO when an amino acid forms a peptide link upon joining the peptide chain. Dipeptides have two amino acid residues, tripeptides have three, tetrapeptides four, and so on. After about 12 residues, this terminology becomes cumbersome, so peptide chains of more than 12 and less than about 20 amino acid residues are usually referred to as oligopeptides, and, when the chain exceeds several dozen amino acids in length, the term polypeptide is used. The distinctions in this terminology are not precise. 

Describe the synthesis of the dipeptide Lys-Ala by Merrifield s solid phase chemical method of peptide synthesis. What pitfalls might be encountered if yon attempted to add a leucine residue to Lys-Ala to make a tripeptide ... 

An exopeptidase that sequentially releases a tripeptide from the N-terminus of a protein or peptide. Tripepti-dyl-peptidases are included in Enzyme Nomenclature sub-subclass 3.4.14 along with dipeptidy 1-peptidases. 

A repeat of hexapeptides is found to be frequent, whereas the repeat of a nonapep-tide is infrequent. The more frequently a single tripeptide occurs, the more frequent is its presence in such larger repeat hexa-, nona-, and higher peptides. 

A general step ahead in polycondensation was achieved by the application of the active ester method by DeTar et al.19) and Kovacs et al.291 Very soon, the nitrophenyl ester, the pentachlorophenyl ester, or the hydroxysucdnimido ester were used exclusively. The esters of the protected tripeptides could be purified by crystallization, then the N-protecting group was split off and the free peptide esters were purified again. Addition of base starts the polycondensation, resulting quickly in the formation of a viscous solution at low temperature. 

Table 2 shows a list of collagen model peptides which have teen prepared. Many efforts have been made to prevent racemization. The polycondensation reaction seemed to be more sensitive to racemization than the coupling steps preparing the monomeric tripeptide. Therefore, the sequence of the monomer was selected with Gly or Pro at the C-terminal chain end, because racemization is mostly favored at the carboxy-activated amino acid, and these amino acids cannot racemize. 

The peptide is removed from the polystyrene resin by means of hydrogen fluoride. The couplings were nearly complete by using a threefold excess of the N-protected tripeptide. A fractionation of the resulting oligotripeptide, however, has been performed. The folding behavior in water was much more pronounced than in the case of the polymers obtained by the old TEPP method13 . 

It is well known that native collagen containes tripeptide sequences, which alone are not capable of building up a triple helix (e.g. Gly-Pro-Leu, Gly-Pro-Ser) when they exist as homopolypeptides. The synthesis of threefold covalently bridged peptide chains opens up the possibility of investigating the folding properties of such weak helix formers, because the bridging reduces the entropy loss during triple-helix formation and thereby increases the thermodynamic stability of the tertiary structure. Therefore, we have... 

In the case of (Ala-Gly-Pro)n with n = 5-15, the tripeptide chains were synthesized by the liquid-solid phase technique. As mentioned above, the coupling of longer preformed peptide chains was difficult and the yield of the trimer was low. Therefore, a liquid-solid phase technique was applied in which a trimer was grown in a stepwise manner, beginning from a trifunctional crosslinked base A. 

In the case of X = Ala, cooperative equilibrium transition curves have been found starting from n = 8 tripeptide units. The reasons for this extraordinary behavior have been discussed concerning the peptide Col 1-3. CD measurements on peptides having chain lengths of 6 and 7 tripeptide units, seem to point out that these peptides are able to form a small amount of triple helix in water near 0 °C. Thus, the sequence (Ala-Gly-... 

Because of these observations, comparative experiments with peptides of different proline content in a solvent less polar than water, are recommended. (Pro-Pro-Gly)n and (Pro-Ala-Gly)n, in methanol/acetic add (volume ratio 9 1) show a temperature-induced triple helix-coil transition which is characterized by the following parameters92,150) (Pro-Pro-Gly)n AH°s = -1.9 kJ/rnol tripeptide AS° = -5.4 J tnor1 K (Pro-Ala-Gly) A HI = -0.9 kJ/mol tripeptide A 5° = -3.8 J mol-1 K ... 

It is known that native collagen contains tripeptide sequences which, because of being homopolypeptides, are not able to give rise to triple-helical tertiary structures (e.g. Gly-Pro-Leu, Gly-Pro-Ser). The reason for this and for the above-mentioned low thermostability of the synthetic homopolypeptides is presumably to be found in the fact that in the case of the model peptides with their monotonously repeated tripeptide sequences, special interactions between the side chains of the different amino acid residues as postulated by Ward and Mason are no more possible157). 

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