Mannans branched-chain

At high temperatures, the Tj values of 13C nuclei of polysaccharides may be sufficiently long to create difficulties in quantitative estimation of integral intensities. Values have been observed, at 25.2 MHz, of 0.27-0.31 s [C-l-C-5 of a-D-(l—>6)-linked D-mannopyranan at 90°], and, for side chains of branched-chain mannans, of 0.22 s [C-l of a-D-mannopyranosyl groups linked (1—>2) to a main chain of (1—>6)-linked-D-mannopyranosyl residues at90°] and of 0.31 s [C-l atoms of2-0-sub-stituted /3-D-mannopyranosyl side-chain units linked (1—>2) to a similar main-chain, at 70°]. Under such conditions, the n.O.e. values are57... 

The possibility of there being branches in the mannan main-chain should not be excluded. Estimates from a number of methylation analyses of galactomannans have shown a slightly higher molar quantity of 2,3-di-O-methyl-D-mannose than 2,3,4,6-tetra-O-methyl-D-galactose53 78,79. However, if branching of the mannan main-chain is a feature of galactomannan structure, its extent seems to be fairly low. 

Mannans of Hansenula capsulata Y-1842 and H. holstii Y-2448 differ structurally from the phosphonomannan components.83 The man-nan of H. capsulata is probably a cell-wall component, and it has the linear, repeating-structure 6. Other Pichia and Hansenula mannans have predominantly linear structures.84 The 13C-n.m.r. spectrum of 6 (see Fig. 2) is distinguishable from that of the branched-chain man-nan85 from Saccharomyces rouxii (repeating unit 7.)... 

Branched-chain mannans from Candida species were analyzed by the methylation technique, and the presence of 2,6-di-O-substituted mannofuranosyl units was suggested on the basis of supposed 3,5-di-O-methyl-D-mannose isolated.100 However, this compound proved to be identical to synthetic 2,4-di-O-methyl-D-mannose,101 and it differed from the authentic 3,5-di-O-methyl isomer,102 which is consistent with 3,6-di-O-substituted D-mannopyranosyl units. 

Yeast mannan is an amorphous, homogeneous polysaccharide with a D. P. of about 500. The proposed structure of this mannan is a long chain, with radiating side-chains of one or two D-mannopyranose units. In this mannan, 2 —> 1, 3 —> 1, and 6 — 1 linkages have been found. The mannan of the seaweed Porphyra umbilicalis contains chiefly 4 —> 1 /3-d linkages, and is of the branched-chain type with about one branch for each 12 D-mannose residues. 

However in the branched chain mannan of fragilis the T- values of main-chain nuclei are 0.09 sec (70°, 25.2 MHz), less than 0.16 sec for the C-1 of the side chain (Fig. 24). Although there was no correspondence of nOe values to segmental motion it was noticeable at 30° that the main chain C-1 signal (12.3 Hz) was broader than that of the side chain signal (8.6 Hz) but this difference decreased on increase of temperature. 

The red seaweed Porphyra umbilicalis, which is widely used as a food, contains a predominantly / -d-(i -> 4)-linked mannan along with other polysaccharides (sulfated galactans). The mannan appears to have a branched chain structure with one branch point for every 12 D-mannose residues. 

The cell wall of the yeast Saccharomyces is rich in mannoproteins that contain 50-90% mannose.264 The 250-residue mannan chains consist of an a-1,6-linked backbone with mono-, di-, and tri-mannosyl branches. These are attached to the same core structure as that of mammalian oligosaccharides. All of the core structures are formed in a similar way.258 265 The mannoproteins may serve as a "filler" to occupy spaces in a cell wall constructed from P-1,3- and P-l,6-linked gly-cans and chitin. All of the four components, including the mannoproteins, are covalently linked together.266 As was emphasized in Chapter 4 (pp. 186-188)... 

Invertase from a Saccharomyces cerevisiae mutant could be separated into two fractions on the basis of solubility in ammonium sulfate.382 The soluble fraction reacted with endo-(l - 6)-a-mannanase, when it became insoluble. The results suggested that the insoluble fraction contained only the highly branched, core section, but the soluble fraction also had the (l->6)-a-D-mannan chain attached. 

The a-(1 3)-hnked D-mannans of Nothogenia fastigiata sulfated on C-2 and C-6 also mimic the minimal binding domain of HS. However, the lower antiviral activity of the fractions with D-xylose side chains suggests that branching precludes binding to the gC viral protein [21],... 

Cell walls of yeasts contain mannans in which the main a-l,6-linked chain carries short branches of one to three mannose units joined in a-1,2, a-1,3, and sometimes a-1,6 linkages. These are covalently linked to proteins. A p-l,4-linked mannan forms microfibrils in the cell wall of some algae such as Acetabu-laria (Fig. 1-11) which do not make cellulose. ... 

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