An arabinogalactan-protein from the pulp of grape berries

Abstract

An arabinogalactan-protein (AGp) was isolated from an aqueous extract of an alcohol-insoluble residue from the pulp of grape berries by ion-exchange and gel-permeation chromatography. AGp contained neutral sugars (89%), mainly arabinose and galactose (mol. ratio, 0.66), uronic acids (3%), and protein (8%), had a weight-average molecular weight ( M w) of 165,000, and treatment with an α- d-arabinofuranosidase released 85% of the arabinose. Methylation analysis of the native and arabinosidase-degraded AGps revealed inner chains of (1→3)-linked galactosyl residues 6-substituted with (1→6)-linked galactosyl residues 3-substituted by terminal arabinosyl units. Reductive alkaline degradation of AGp showed that the threonine residues were involved in carbohydrate-protein linkages.