Linkage types

Single linkage type. Several of these are neutral glucans, eg curdlan. Others are polyanionic homopolymers and, unlike the glucans, also contain acyl groups. 

Figure 7.2 Three main types of homopolysaccharides, a) Single linkage type, eg curdlan. b) Side chain type, eg scleroglycan. c) Branched chain type, eg dextran. The figure also show various ways of illustrating exopolysaccharida structure.

Cyclic oligosaccharides composed of a single type of residue can be named by giving the systematic name of the glycosyl residue, preceded by the linkage type in parentheses, preceded in turn by cyclo- with a multiplicative suffix (i.e. cyclohexakis- etc.)... 

Xylans as true homopolymers occur in seaweeds of the Palmariales and Nemaliales, however, their backbone consists of Xylp residues linked by -(1 3) (Type X3, Fig. la) or mixed -(1 3, 1 -> 4)-glycosidic linkages (Type Xmy Fig. lb). They are assumed mainly to have a structural function in the cell-wall architecture, but a reserve function cannot be ruled out [4]. From the microfibrils of green algae (Siphonales) such as Caulerpa and Bryop-sis sp., X3 was isolated and the structure confirmed by methylation analysis, C-NMR spectroscopy [7], as well as by mass spectrometry of enzymically released linear oligosaccharides up to a degree of polymerization (DP) of... 

Polymer Linkage-Type and Alignment of Amino Acid Sequences of Various (Mutant) Glucansucrase Enzymes with GTFR Wild-Type and Mutant Variants58... 

The integral intensities of signals of polysaccharides, obtained with a modem spectrometer under the usual operating conditions, are proportional or quasi-proportional, to the number of 13C nuclei present. This has been observed, in particular, in the case of linear hexo-pyranan structures containing one type,11,47,51,55,56 58-61 or two equal types, of linkage,62 or branched-chain polymers having two linkage types,53,58 where the resonances are readily resolved. In such cases, the T values would be low, 0.2 s or less, and the n.O.e. values would be approximately equal. However, few actual determinations of these values have been made, and extrapolation of such assumptions to more-complex polysaccharide structures is not recommended, as outlined in Section V,2,... 

The majority of ascomycetous yeasts form cell-wall mannans or ga-lactomannans having main chains of (1— 6)-linked a-D-mannopyrano-syl residues, often substituted at 0-2 by a-linked glycosyl groups. The linkage types in the rest of the side chains vary widely, and can consist of 2-O-substituted a- or /3-D-mannopyranosyl residues, or 3-O-substi-... 

Figure 3.2 The main linkage types in softwood and hardwood lignin.

Nature and linkage type of acyl substituents of the lipid A backbone bound to ... 

Such Tj measurements have also been employed to differentiate between terminal and branch-point residue resonances for dextrans branching through the 4,6-di- -substituted a-D-glucopyranosyl residue and for establishing that the excess 6-0-substituted a-D-glucopyranosyl residues of the class of compounds represented by structure 3 are in side chains relative to an alternating linkage type backbone (13). 

Structural analysis of isolated amylose and amylopectin components has been carried out by standard methods based on methylation, periodate oxidation, and partial acid hydrolysis studies. Methylation and periodate oxidation studies established the linkage types and frequency of... 

The differences in the rates of hydrolysis of various linkage types by a particular glycosidase can be used to provide information about this aspect of structure. Jack-bean a-D-mannosidase cleaves a-(l- 2) and a-(l- 6) linkages much faster than a-(l -> 3). Oligosaccharides, obtained by endo-N-acetyl-/J-D-glucosaminidase hydrolysis of ovalbumin, were subjected to acetolysis, which selectively cleaved the a-(l - 6) bonds. A tetrasaccharide isolated after this treatment was then incubated with jack-bean o-d-... 

Enzymic hydrolysis of dextrans has provided information both on the linkage types and the disposition of different linkages as established by methylation. Since the publication of the earlier article,1 enzymic studies on Leuconostoc dextrans have continued, and investigations of Streptococcus a-D-glucans have shown that there are significant, structural differences between some of these and those of Leuconostoc spp. Reviews on dextrans have appeared.419,420... 

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