Complex carbohydrates, composition

Abstract To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues. 

In general the sphingolipids are located on the exterior face of a membrane while the phospholipids make up the inner face. This is understandable when we recall that sphingolipids include the gangliosides and cerebrosides whose polar ends contain carbohydrates or complex carbohydrate derivatives. The large number of chiral centers in carbohydrate molecules offer a complex pattern on the surface of the membrane which can impart a large degree of specificity for a particular cell type. The composition and limited fluidity of the bilayer make the entire membrane asymmetric, that is, different on the inner and outer layers or leaflets. 

Fig. 7. (A) A detailed model of the amino-terminal al(IV) and a2(IV) chains containing the 7 S domain and an adjacent segment of the main triple helix. The terminal sequence of both chains is nonhelical and contains lysines (K), hydroxylysines (K), and cysteines (C) that participate in intra- and intermolecular cross-linking. A helical cross-linking site is located about 30 nm from the amino terminus (N) of the molecule and contains cysteines and a hydroxylysine in the al(IV) chain involved in cross-linking plus a complex carbohydrate attachment site (CHO). The cap site within the main triple helix identifies a series of four triplets containing proline (P) and hydroxyproline (P), a composition that would be expected to form a very stable helical structure, [Data from Glanville et al. (1985) Siebold et al. (1987)]. (B) The antiparallel arrangement of type IV molecules with alignment of cross-linking sites.

Although a monoclonal antibody is considered to consist of a single molecule, in reality this is not the most frequent case. Due to posttranslatorial modification, especially glycosylation,12,13 a family of molecules with identical aminoacid backbone, but different carbohydrate composition, is generated.14,15 The possible structure of N-linked oligosaccharides of the complex types is shown in Fig. 3. 

Enzyme-lectin histochemistry has many features in common with EIH. Lectins are of non-immune origin but recognize fine differences in complex saccharide structures. Usually lectin specificity is expressed as reactivity to a given monosaccharide, but it has been demonstrated repeatedly (e.g.. Debray et al., 1981) that this is an oversimplification (Section 3.4). It is becoming increasingly clear that cellular differentiation, maturation and neoplastic transformation are associated with changes of carbohydrate composition of the cell membrane (Ponder, 1983). 

Heparin, then, consists of a series of highly sulfated compounds, identical in carbohydrate composition but separated by complexing with LKB ampholyte (with progressive adjustment of pH), into a large number of separate chains. These chains are flexible molecules, probably in a Gaussian coil, and are characterized by a shell of negative charges... 

Between 45-75% of the total solids in the citrus peel and membrane has been found to be insoluble in alcohol (Table II), and the main portion of this alcohol-insoluble material is complex carbohydrate (. The alcohol-insoluble solids (AIS) of the coarse pulp Is also largely complex carbohydrate, and It also contains proteins and Inorganic salts ( ). Of the complex carbohydrates, pectin Is by far the most Important fraction. Rouse et al. (7) divided the pectlc substances into water soluble, oxalate soluble, and sodium hydroxide soluble fractions in their study. Eaks and Sinclair ( ) found a difference in the composition of the hemlcellulose-cellulose fraction between the mature and Immature Valencia orange peel AIS. 

The purpose of this work Is to study the composition of the residues from citrus processing and to devise a method for separating and estimating the nature and quantities of various fractions of the complex carbohydrates from such materials. 

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