A- Amino Acids, Peptides, and Proteins

The following two sections illustrate how a knowledge of the acid-base properties of amino acids and peptides can be used to advantage in designing separation procedures, or predicting separation patterns. 

Ion-exchange chromatography is widely used to separate and analyze mixtures of amino acids. The most common ion-exchange resin used for this purpose is a sulfonic acid cation exchanger of the Dowex-50 (polystyrene) type. The structure of the resin is  

A rapid estimate of the effective charge on an amino acid can be made by comparing its pi with the pH of the buffer used  

If Ap is positive, the amino acid carries a net positive charge. An amino acid with a greater Ap will stick more tightly to a cation-exchange resin than an equally hydrophobic amino acid with a lower Ap. If Ap is negative, the 

A solution containing aspartic acid (pf = 2.98), glycine (pi 5.97), threonine (pi = 6.53), leucine (pi = 5.98), and lysine (pi — 9,74) in a pH 3.0 citrate buffer was applied to a Dowex-50 cation-exchange column equilibrated with the same buffer. The column was then eluted with the buffer and fractions collected. In what order will the five amino acids elute from the column  

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I inhydrin-Color Reaetion, This reaction is commonly used for qualitative analysis of a-amino acids, peptides, and proteins. 

The data presented in Table 3.1 demonstrate that 0.3% (w/v) ninhydrin has a marked effect at pH 5.0 on bubble production in agarose gels containing distilled water. This concentration of ninhydrin reduced bubble production at pH 5.0 to only one third of that observed in the control buffered at the same pH, whereas no significant effect at pH 8.0 was observed (Table 3.1). This pH dependence of the chemical effect is important for the reason that ninhydrin is known to react appreciably with a-amino acids, peptides, and proteins in various buffered aqueous solutions ranging in pH from 5.0 to a maximum of 7.0 (ref. 232,233) and specifically in aqueous solutions containing citrate buffer (as used in this study) at pH 5.0 (ref. 233). While ninhydrin is also known to react with many amino compounds and ammonia (ref. 233), such interfering... 

Barakat et al. observed that on treatment with NBS in aqueous solution an a-amino acid (alanine) and a dicarboxylic acid (oxalic) undergo decarboxylation with liberation of bromine. Luck showed that a-amino acids, peptides, and proteins on treatment with NBS (2 equiv.) in aqueous solution undergo quantitative decarboxylation. The reaction is complete in 30 min. with quantitative evolution of COj, as determined in a Warburg apparatus. The first stable product formed is the aldehyde. 

In a survey of the methods used for peptido synthesis in 1968, the isoxazolium salt method was used in 7% of the examples surveyed J. H. Jones in Amino Acids, Peptides, and Proteins, Vol. 2, The Chemical Society, London, 1970, p. 145. 

Spatola, A. F., Peptide backbone modifications, in Chemistry and Biochemistry of Amino Acids. Peptides, and Proteins (B. Weinstein, ed.), Marcel Dekker, New York, 1983, pp. 268-357. 

Sweetness is a quality that defies definition, but whose complexity can be appreciated merely by examining the molecular structures of those compounds that elicit the sensation. They come in all molecular shapes and sizes, and they belong to such seemingly unrelated classes of compounds as aliphatic and aromatic organic compounds, amino acids, peptides and proteins, carbohydrates, complex glycosides, and even certain inorganic salts. 

Depicted in Fig. 2, microemulsion-based liquid liquid extraction (LLE) of biomolecules consists of the contacting of a biomolecule-containing aqueous solution with a surfactant-containing lipophilic phase. Upon contact, some of the water and biomolecules will transfer to the organic phase, depending on the phase equilibrium position, resulting in a biphasic Winsor II system (w/o-ME phase in equilibrium with an excess aqueous phase). Besides serving as a means to solubilize biomolecules in w/o-MEs, LLE has been frequently used to isolate and separate amino acids, peptides and proteins [4, and references therein]. In addition, LLE has recently been employed to isolate vitamins, antibiotics, and nucleotides [6,19,40,77-79]. Industrially relevant applications of LLE are listed in Table 2 [14,15,20,80-90]. 

Aguilar, M. I., Hodder, A. N., and Hearn, M. T. W., High-performance liquid chromatography of amino acids, peptides, and proteins. LXV. Studies on the optimisation of the reversed-phase gradient elution of polypeptides. Evaluation of retention relationships with (3-endorphin-related polypeptides, /. Chromatogr., 327, 115, 1985. 

Separation of amino acids, peptides, and proteins Amino acids are interesting molecules by themselves from an analytical point of view for two reasons. They are inherently enantiomeric and are the building blocks of peptides and proteins. The separation of amino acids is usually done through a derivatization process due to the fact that the absorbance in the UV is low. The most frequently used derivatization is done by fluorescent tagging. Sensitivity can reach the subfemtomole level.136 139 Temperature control can be used to separate conformers.140 Two conformers of Tyr-Pro-Phe-Asp-Val-Val-Gly-NH2 and four conformers of Tyr-Pro-Phe-Gly-Tyr-Pro-Ser-NH2 were separated at subzero temperatures by including glycerol as an antifreeze component of the buffer. 

In this section, the structure, function, and reactivity of amino acids, peptides, and proteins will be discussed with the goal of providing a foundation for successful derivatization. The interplay of amino acid functionality and the three-dimensional folding of polypeptide chains will be seen as forming the basis for protein activity. Understanding how the attachment of foreign molecules can affect this tenuous relationship, and thus alter protein function, ultimately will create a rational approach to protein chemistry and modification. 

The composite model is a combination of the monoparametric v model with the simple branching model. This method has proven useful in modelling amino acid, peptide and protein properties49. It is an improvement over the simple branching model and requires only one additional parameter. 

Various important LC methods for amino acid, peptide and protein analysis were reviewed and evaluated126,127. A review of HPLC methods for the analysis of selected biogenic amines in foods appeared, including methods for extraction and for elimination of interfering compounds128. 

A comparison of the mean amino acid composition of the soils with those of algae, bacteria, fungi, and yeasts showed the greatest similarity to that of bacteria. [4] This suggests, perhaps not too surprisingly, a major role for microorganisms in the synthesis in the soil of amino acids, peptides and proteins from plant and animal residues, and also explains the relatively uniform amino acid composition in different soils. 

Yarovsky, L, Aguilar, M.I., and Hearn, M.T.W., High-performance liquid-chromatography of amino-acids, peptides and proteins. 125. Molecular-dynamics simulation of n-butyl chains chemically bonded to sihca-based reversed-phase high-performance liquid-chromatography sorbents, 7. Chromatogr. A, 660, 75, 1994. 

These basic concepts are followed by a section on the structure of the important biomolecules (pp. 34-87). This part of the book is arranged according to the different classes of metabolites. It discusses carbohydrates, lipids, amino acids, peptides and proteins, nucleotides, and nucleic acids. 

H., Hayes., T. and Gathergood., N. (2009) (ed A.B. Hughes) Amino Acids, Peptides and Proteins in Organic Chemistry. Volume 2 — Catalysis of Reactions by Amino Acids Wiley-VCH Verlag GmbH, Weinheim, pp. 283-337 (d) Gathergood, N. (2002) Asymmetric organocatalysis proline an essential amino-acid Aust. J. Chem.,... 

In heavily sulfited white wines containing over 0.5 ppm copper and stored in sealed containers, a reddish-brown deposit may form. This occurs in the absence of oxygen and ferric ions but redissolves readily upon exposure to oxygen. Its formation may be accelerated by exposure to sunlight or heat, and it is believed to consist of colloidal cupric sulfide (14, 29). More commonly, copper casse may arise from reactions between copper and sulfur-containing amino acids, peptides, and proteins (15,16,17). 

Spatola, A. E, In Chemistry and Biochemistry of Amino Acids, Peptides and Proteins, Weinstein, B., Ed. Marcel Dekker New York,... 

Relevant original papers are to be found in a wide range of journals covering many disciplines. Consequently, considerable use has been made of the excellent review series edited by Sigel1 and of the annual review2 Amino Acids, Peptides and Proteins interested readers are referred to these for up-to-date information. 

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