Peptides naturally occurring

Uncommon Amino Acids Found in Naturally Occurring Peptides 

Principal carbon chain Amino acid Peptide References 

c-Diaminopimelic acid Peptide attached to a lipo-polysaccharide isolated from M. tuberculosis (30) 

Naturally occurring peptides are of great interest, since amino acids form the building blocks not only for the synthesis of proteins but also for a whole series of peptides which often possess extremely potent biological activity such as antibiotics, hormones, toxins, and growth factors. 

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Melanocortins. Figure 1 Shows the melanocortin receptors, function and naturally occurring peptide sequences that activate them. 

O DONAHUE has isolated a naturally occurring peptide from brain that can produce responses similar to PCP when administered to animals. The results are reminiscent of the early studies of the opiopeptides that interact with opiate receptors and produce effects like narcotic drugs when administered to animals. 

Erspamer Y, Melchiorri P, Falconieri-Erspamer G, et al. Deltorphins a family of naturally occurring peptides with high affinity and selectivity for opioid binding sites. Proc Natl Acad Sci USA 1989 86 5188-5192. 

Libraries can also be made from naturally occurring peptides (e.g. melanocortin [30] and somatostatin [31]) and their variants, or be derived from protein-fragments. The former have been employed mainly for the identification of peptide variants with unproved characteristics, and the latter for the identification of antigenic determinants present on targets, for example by selecting for binders to monoclonal antibodies specific for an antigen-fragment peptide library. 

Naturally occurring peptides can be altered in size and structure, and randomization of residues can be introdnced into libraries for the identification of peptides with improved characteristics or improved binding specificity. Snch an approach has been used to select re-ceptor-spedfic variants of atrial natrinretic peptide (ANP) with improved expression in E. coli and spedficity for jnst one form of the ANP receptors [29]. 

Analogues in which one or more of the naturally occurring peptide bonds in a substrate, effector, or ligand has been replaced by some other chemical structure. Such compounds are useful in characterizing binding specificity (particularly conformational specificity), and... 

This chapter commences with Section 7.1 which deals with reversed-phase chromatography (RPC) and related techniques as applied to synthetic peptides 1-3 A detailed discussion on RPC is presented. Basic considerations are covered as are issues of fundamental physical chemistry. Many examples of chromatography and quantitative relationships are described for peptides and peptide derivatives. There is also an extensive table of naturally occurring peptides that have been isolated and purified by RPC techniques. The section includes many examples of RPC and HPLC profiles of peptidic systems. 

Results comparable to those shown in Figure 1 can readily be achieved with most crude mixtures containing synthetic or naturally occurring peptides, using similar RPC strategies. The resolution of synthetic peptides prepared by solid- or solution-phase chemical methods is now so routine by analytical and preparative RPC methods that an April 2000 CD-ROM database search of relevant scientific journals revealed that over 2500 publications arise each year on the use of RPC for the purification or analysis of peptides as part of the scientific literature related to peptide chemistry and its application in various fields of the biomedical or biological science and in biotechnological applications related to the food, environmental, and pharmaceutical industries. 

Table 4 Illustrative Examples of Synthetic and Naturally Occurring Peptides Isolated by RPC Procedures...

The application of high-performance capillary zone electrophoresis (HP-CZE) in its various selectivity modes has become a very valuable adjunct to HPLC for the analysis of peptides. For synthetic peptides, in particular, both HPLC and HP-CZE now form essential components of the analytical characterization of these molecules. Increasingly, zonal, micellar, or (biospecific) affinity-based HP-CZE procedures with open tubular capillary systems are adapted to allow resolution with extremely high separation efficiencies (e.g., >105 plates per meter) of synthetic or naturally occurring peptides as part of the determination of their structural, biophysical, or functional properties. Illustrative of these capabilities are the results shown in Figure 19 for the separation of several peptides with different charge and Stokes radius characteristics by HP-CZE. 

The flavor enhancer monosodium glutamate (MSG) is currently used in virtually every type of savory prepared-food. Unfortunately, MSG has several deleterious side effects on a large proportion of the population. Fortunately, a naturally occurring peptide isolated from a muscle food (beef) can serve not only as a potential replacement for MSG but also as a nutritional adjuvant. The peptide, called BMP or beefy meaty peptide, acts as a flavor enhancer and is found to occur naturally in beef Chapter 6). Research on BMP suggest that it is not only non-allergenic but, by virtue of its protein composition, is a nutritionally sound replacement for MSG. 

Erspamer, V., Melchiorri, P., Falconieri-Erspamer, G., Negri, L., Corsi, R., Severin , C., Barra, D., Simmaco, M., Kreil, G. Deltorphins a family of naturally occurring peptides with high affinity and selectivity for Sopioid binding sites, Proc. Natl. Acad. Sci. USA 1989, 86, 5188-5192. 

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