Structural studies of plant gum from sap of the lac tree, Rhus vernicifera

Abstract

The plant gum isolated from sap of the lac tree, Rhus vernicifera (China), was separated into two fractions having mol. wt. 84,000 and 27,700 by aqueous-phase gel-permeation chromatography. The fractions contain d-galactose (65 mol%), 4- O-methyl- d-glucuronic acid (24 mol%), d-glucuronic acid (3 mol%), l-arabinose (4 mol%), and l-rhamnose (3 mol%). Smith degradation of the carboxyl-reduced polysaccharides gives products of halved molecular weight, and these consist of a β-(1→3)-linked galactopyranan main chain and side chains made up of galactopyranose residues. Peripheral groups, such as α- d-Gal p-, α- d-Gal p-(1→6)-β- d-Gal p-, 4- O-methyl-β- d-Glc pA-, and 4- O-methyl-β- d-Glc pA-(1→6)-β- d-Gal p-, are attached to this interior core through β-(1→3)- or β-(1→6)-linkages.