Galactan Backbone Research Articles

Polysaccharides leached from the surface of pea endocarp

Polymers (apparent M r 1.1–1.23 x 10 6) containing ca 80% carbohydrate and 16% protein are leached by water from the surface of pea endocarps. These polymers were examined by hydrolysis, methylation analysis and Trisacryl gel column chromatography and were found to be primarily acidic arabinogalactans (Type II) with a 3-linked galactan backbone branched through C-6 to side chains of 6-linked galactopyranose terminating in 4- O-methyl glucuronic acid and arabinofuranose residues. The main polymeric component obtained by gel filtration of the polymers gave a positive reaction to the presence of the β-glucosyl Yariv antigen. The presence of small amounts of xyloglucans and xylans was suggested by the detection of 4,6-linked glucopyranose and 4-linked xylopyranose residues. Pectic polysaccharides were suggested by the presence of 5-linked arabinofuranose and 4-linked galacturonic acid residues. Inoculation of pea endocarps with a conidial suspension of Monilinia fructicola resulted in reduced amounts of 4-linked galacturonic acid residues.

Structural features of the acidic polysaccharide of Spondias pinnata gum exudate

The purified, homogeneous, acidic polysaccharide isolated from the gum exudate of Spondias pinnata, and its degraded product prepared by controlled autohydrolysis, were found to contain d-galactose, l-arabinose, and d-galacturonic acid. Complete methylation followed by hydrolysis, both before and after reduction with lithium aluminum hydride, revealed the probability of a (1 →3)-linked, galactan backbone. The linkages of the interior parts were confirmed by methylation studies, and by the results of periodate oxidation and Smith degradation.

Structural studies on the major component of Gladiolus style mucilage, an arabinogalactan-protein.

The major component of the Gladiolus style mucilage was shown to be an arabinogalactan-protein. The arabinogalactan-protein was isolated from the style extract by affinity chromatography with tridacnin (the galactose-binding lectin from the clam Tridacna maxima) coupled to Sepharose 4B. The isolated arabinogalactan-protein represents 40% of the soluble style extract; it contains 90% (w/w) carbohydrate and 3% protein. The major monosaccharides of the carbohydrate component are galactose and arabinose, in the proportions 6:1. A component with a similar composition was also isolated from the crude extract by precipitation with the beta-glucosyl artifical carbohydrate antigen. The protein moiety of the arabinogalactan-protein remained associated with the carbohydrate after chromatography in urea, and has high contents of serine, glutamic acid, aspartic acid, glycine and alanine. The arabinogalactan-protein is apparently chemically homogeneous; it eluted as a single symmetrical peak from Sepharose 4B, and three fractions collected across the peak were structurally similar. Ultracentrifugal studies showed it to be polydisperse in the mol.wt. range 150 000--400 000. The information obtained from methylation analyses, oxalic acid and enzymic hydrolyses is consistent with a model having a beta 1 leads to 3 galactan backbone, branched through C(O)6 to beta 1 leads to 6 galactan side chains. The arabinose is exclusively present as terminal alpha-L-arabinofuranosyl residues. Enzymic removal of the arabinose residues resulted in a marked decrease in solubility of the molecule. The localization of the arabinogalactan-protein in the mucilage of the style canal was demonstrated cytochemically. The possible roles of the arabinogalactan-protein in relation to recognition of compatible pollen and pollen-tube growth are discussed.