Complex mixtures, protein components

Unlike the simple example of the solution described above, a human body is a complex mixture of components (tissues, proteins, membranes, etc.). Yet, in human pharmacokinetic studies, with rare exceptions only the plasma... 

Nearly all foods are made up of a complex mixture of components, including carbohydrates, amino acids, and proteins. When these foods are heated, the Maillard reaction occurs resulting in the formation of a large variety of volatile flavor compounds (1-3). The Maillard reaction is responsible for both desirable and undesirable aromas in foods. The aroma of bread, chocolate, coffee, and meat are all examples of desirable aromas resulting from the Maillard reaction. The aromas of burned food, canned products, stale milk powder, cereal, and dehydrated potatoes are typical examples of the undesirable aspects of this reaction. 

Individual ammo acids differ m their acid-base properties This is important m peptides and proteins where the properties of the substance depend on its ammo acid constituents especially on the nature of the side chains It is also important m analyses m which a complex mixture of ammo acids is separated into its components by taking advantage of the differences m their proton donating and accepting power... 

The importance of linked scanning of metastable ions or of ions formed by induced decomposition is discussed in this chapter and in Chapter 34. Briefly, linked scanning provides information on which ions give which others in a normal mass spectrum. With this sort of information, it becomes possible to examine a complex mixture of substances without prior separation of its components. It is possible to look highly specifically for trace components in mixtures under circumstances in which other techniques could not succeed. Finally, it is possible to gain information on the molecular structures of unknown compounds, as in peptide and protein sequencing (see Chapter 40). 

Ribbon views of proteins with varying amounts of helices and pleated sheets. Immunoglobulin, an antibody, is made up almost entirely of pleated sheets (magenta). Myoglobin, which stores oxygen in muscle tissue, is composed of about 70% helix (blue). G-Actin, a component of muscle protein fibers, is a complex mixture of helices and pleated sheets. Regions with no specific secondaiy stmcture are shown in orange. 

Plants were probably the first to have polyester outerwear, as the aerial parts of higher plants are covered with a cuticle whose structural component is a polyester called cutin. Even plants that live under water in the oceans, such as Zoestra marina, are covered with cutin. This lipid-derived polyester covering is unique to plants, as animals use carbohydrate or protein polymers as their outer covering. Cutin, the insoluble cuticular polymer of plants, is composed of inter-esterified hydroxy and hydroxy epoxy fatty acids derived from the common cellular fatty acids and is attached to the outer epidermal layer of cells by a pectinaceous layer (Fig. 1). The insoluble polymer is embedded in a complex mixture of soluble lipids collectively called waxes [1], Electron microscopic examination of the cuticle usually shows an amorphous appearance but in some plants the cuticle has a lamellar appearance (Fig. 2). 

Natural biological membranes consist of lipid bilayers, which typically comprise a complex mixture of phospholipids and sterol, along with embedded or surface associated proteins. The sterol cholesterol is an important component of animal cell membranes, which may consist of up to 50 mol% cholesterol. As cholesterol can significantly modify the bilayer physical properties, such as acyl-chain orientational order, model membranes containing cholesterol have been studied extensively. Spectroscopic and diffraction experiments reveal that cholesterol in a lipid-crystalline bilayer increases the orientational order of the lipid acyl-chains without substantially restricting the mobility of the lipid molecules. Cholesterol thickens a liquid-crystalline bilayer and increases the packing density of lipid acyl-chains in the plane of the bilayer in a way that has been referred to as a condensing effect. 

Lins et al. 127 have studied five peptide sequences derived from the ApoB-100 protein, which is the protein moiety in low-density lipoproteins (LDC) that transport cholesterol. ApoB-100 is insoluble and binds to the surface of the LDC particle, and these selected sequences for this study have been implicated as being important in the lipid binding. ATR-FTIR studies showed the one core and three C-terminal originating sequences were mostly sheet-like in the presence of unilamellar vesicles but the N-terminal one was different, probably representing a complex mixture of conformers with some helical component. Furthermore, these workers were able to carry out ATR-LD measurements and determine the orientation of the peptide as being oblique to the membrane. These studies are in contrast to ultraviolet ECD results which were adversely affected by scattering artifacts. 

Since gel permeation discrimination depends on Re, it is apparent that dramatically enhanced resolution is obtainable in 6M GuHCl. This factor has led to the use of this technique for analysis of such complex mixtures as proteolytic digestion products (12,13) and red cell membrane proteins (14). An added dividend of the method is recovery of the isolated polypeptide components for further physical or chemical studies. 

Soybeans and soybean products contain high levels of protein, carbohydrates, and lipids (Table 11.6.1). As minor components of complex mixtures, isoflavones must first be separated from the bulk of the matrix constituents prior to analysis. Efficient extraction methods for isoflavones should account for their diverse structures, chemical properties, and the food matrix of which they are constituents. This unit describes a practical way of extracting isoflavones from soybean products in their natural forms using readily available solvents and laboratory equipment. 

The natural world is one of complex mixtures petroleum may contain 105—106 components, while it has been estimated that there are at least 150 000 different proteins in the human body. The separation methods necessary to cope with complexity of this kind are based on chromatography and electrophoresis, and it could be said that separation has been the science of the 20th century (1, 2). Indeed, separation science spans the century almost exactly. In the early 1900s, organic and natural product chemistry was dominated by synthesis and by structure determination by degradation, chemical reactions and elemental analysis distillation, liquid extraction, and especially crystallization were the separation methods available to organic chemists. 

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