Structural elucidation of proteic fraction isolated from Acacia glomerosa gum

Acacia glomerosa Benth., Venezuelan Vulgares species, exudates a clear gum, which is able to produce a gel easily. Physico-chemical data of this gum, except the nitrogen content, are very close to those reported for Acacia senegal gum. The gum samples (untreated and treated with alkali) were studied by size exclusion chromatography on a packed column with Fractogel S-60, using 0.1 M NaCl as eluent. The elution profiles of protein and carbohydrate fractions were determined at 220 and 490 nm, respectively. The elution profiles of the original gum (untreated gum) showed a high molecular weight fraction, rich in protein and carbohydrate, which may correspond to an arabinogalactan–protein (AGP) complex. Other peaks were also observed of higher elution volume that may probably be peptides. The presence of the AGP was also observed in the elution profile of the gum after basic treatment. Sugar and amino acid composition of five fractions, containing carbohydrate and protein, were studied. On the other hand, sugar and amino acid composition were determined on the A. glomerosa gum and its degraded products. The results obtained so far suggest that the gum from A. glomerosa is a mixture of polysaccharide and arabinogalactan–protein. Approximately 18% of this gum is protein, which is characteristically rich in hydroxyproline, leucine, serine and threonine.