The distribution of d-galactosyl groups in guaran and locust-bean gum: new evidence from periodate oxidation

Abstract

A detailed theoretical analysis of the kinetics of the periodate oxidation of guaran and locust-bean gum, together with the results of methylation analyses carried out by Lindberg's group on partially oxidised and barohydride-reduced samples of the galactomannans, has provided new evidence for the arrangement of the α- d-galactopyranosyl side-groups along the mannan chains. The results indicate that, in guaran, the d-galactosyl groups are arranged in small groups of mostly two to four units, attached to contiguous d-mannosyl residues in the chains. These are separated mostly by small groups of two, or occasionally three, contiguous, unsubstituted d-mannosyl residues. In locust-bean gum, there are long blocks of contiguous, unsubstituted d-mannosyl residues, long blocks in which every second d-mannosyl residue is substituted with d-galactose, and shorter blocks in which there is a high density of d-galactosyl groups.