Structure of Galactomannans and Related Polysaccharides

A further conclusion from the inethylation results was that approximately 6% of the residues in the mannan backbone are (1 — 2)-linked. Single D-galactosyl stubs are linked to the main chain by (1 — 6)-bonds. 

In a similar series of experiments, Unrau and Choy59 found that the structure of Caesalpinia pulcherima galactomannan differs from the normal type of structure, but to a much lesser extent —4% of the D-mannose units in the main chain are /3-D-(l — 3)-linked, and 2% are ( 1 — 2)-linked. Smith degradation again indicated that isolated and consecutive /8-D-(l — 3)-linkages were present in the main chain. 

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. 

Although most of the galactomannans studied are reported to have structures based on a completely /3-D-(l — 4)-linked backbone having single a-D-galactosyl stubs attached to this backbone by (1 — 6)-linkages, the reports just discussed indicate that deviations, sometimes substantial, can occur. Indeed, it is possible that deviations from the classical type of structure, to the extent shown by Caesal- 

Analogies may be drawn between galactomannans and xylo-glucans. The latter polysaccharides, often referred to as amyloids, are found in seed endosperms of plants from many different fami- 

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