Short peptides

As an alternative strategy, prelipidated building blocks can be used to generate prenylated peptides (Scheme 8). Thereby advantage is taken of the stability of the thioether linkage that offers the possibility of applying, for example, the Fmoc strategy for such peptides. Short N-Ras C-termini, for example, are readily available via this method. ... 

Peptides—Short chains of amino acids small proteins. 

We have recently reported a decreased fraction of A 5l-42 of all A(i peptides in C S E of patients with AD. In this study, all the AD patients and none of the controls appeared below the discrimination line of 8.5%. Plotting the results of relative ratios of A(il-42 against A(il-38 showed all AD cases and none of the controls in the region with decreased A(il-42 however some AD cases had increased A 5l-38, similarly to subjects with chronic neuroinflammatoiy diseases (Wiltfang et al., 2002) (figure 14.3). This observation points to a presence of chronic (micro)-inflammatory reaction in the CNS of subjects with AD. Moreover, this report also presents evidence that severity of dementia correlates negatively with percentage but not absolute value of A(i peptides shorted at their carboxyl ends. 

The first synthesis reported by Merrifield produced the desired tetrapeptide (Leu-Ala-Gly-Val).f l Amino acids, dipeptides, and tripeptides were all detected in the crude product released from the resin. Through continued improvements of the method, the high speed of the amino acid incorporation and automation, the solid-phase peptide synthetic methodology has become the method of choice for most laboratories synthesizing peptides. Shortly after the introduction of the solid-phase procedure it was used to synthesize insulin. This impressive achievement awakened the biochemical community to the promise of synthetic chemistry and initiated a period in which large numbers of peptide analogues were prepared and analyzed. 

Peptide Short, linear polymers of alpha-amino acids formed by covalent bonds... 

Peptides (short chains of amino acids, see Section 3.6.3), comprise the classes of hormones, neurotransmitters, endorphins, and growth factors. They are produced and stored in the nervous system, endocrine system, and immune system (Capra, 1996). They are physiologically active, and increase attention, raise glucose levels, increase heart rate, and deaden pain, among others. 

Proteins and peptides (short proteins) are polymers of amino acids joined by amide groups. One feature common to the structure of many proteins is the j8 sheet, shown... 

Miick S M, G V Martinez, W R Fiori, A P Todd and G L Millhauser 1992. Short Alanine-based Peptides Ma Form 3(10)-Flelices and not Alpha-helices in Aqueous Solution. Nature 359 653-655. 

Short chains of amino acid residues are known as di-, tri-, tetrapeptide, and so on, but as the number of residues increases the general names oligopeptide and polypeptide are used. When the number of chains grow to hundreds, the name protein is used. There is no definite point at which the name polypeptide is dropped for protein. Twenty common amino acids appear regularly in peptides and proteins of all species. Each has a distinctive side chain (R in Figure 45.3) varying in size, charge, and chemical reactivity. 

Peptidoplycans (14,16) are the primary component of bacterial cell walls. They consist of a heteropolysaccharide called murein cross-linked with short peptide chains. 

The proteins in food supplements are often hydrolyzed to short peptides to make them easier to absorb. A high content of amino acids is deleterious, however. Thus, there is ongoing interest in determining the size distribution of peptides in protein hydrolyzates. Silvestre et al. (29,30) used a PolyHEA column to compare casein hydrolyzates prepared through various methods. They were able to assess the content of the smallest peptides, as well as amino acids (Fig. 8.13). 

Superose gel material of Pharmacia Biotech is a highly epichloro-hydrine cross-linked agarose matrix that has a pH range of 3-12 (short term 1-14). Hydrophilic interactions may be noticeable for lipids, peptides, and small aromatic compounds, but such interactions might even improve resolution. Superose medium is available in two different porosities Superose 6 HR 10/ 30 (bead size 13 2 /um maximum pressure 1.5 MPa) and Superose 12 HR 10/30 (bead size 10 2 /um maximum pressure 3.0 MPa). 

Cell wall Peptidoglycan a rigid framework of polysaccharide cross-linked by short peptide chains. Some bacteria possess a lipopolysaccharide- and protein-rich outer membrane. Mechanical support, shape, and protection against swelling in hypotonic media. The cell wall is a porous nonselective barrier that allows most small molecules to pass. 

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. 

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