Acacia macracantha gum as a possible source of arabinogalactan–protein

Acacia macracantha, a Venezuelan Gummiferae species, exudes a soluble gum which has a very high polydispersity index (Mw/Mn = 3.75). It consists of carbohydrate predominantly and a proteinaceous material as a minor component. The relatively high nitrogen content (4.98%) led to study the latter material. Fractionation of the gum by atmospheric pressure size exclusion chromatography (APSEC) was monitored by determination of total protein and carbohydrate contents. High pressure exclusion chromatography (HPSEC), coupling on-line with multi-angle light scattering (MALLS) and differential refractive index (DRI) detectors were also used. The elution profiles of the original gum and those of the gum after basic and enzymatic hydrolyses showed a heterogeneous system. Studies of the highest molecular weight fraction, that contain carbohydrate and protein, revealed the presence of hydroxyproline, serine, and lysine. On the other hand, sequential acid hydrolysis study of this fraction demonstrated the presence of rhamnose and arabinose as terminal and internal residues, respectively. The findings suggest that the gum from A. macracantha contains probably AG and AGP.