CHARACTERIZATION OF GUM-ARABIC FRACTIONS OBTAINED BY ANION-EXCHANGE CHROMATOGRAPHY

Two samples of authentic gum arabic (A and B) have been fractionated b y anion-exchange chromatography on DEAE-cellulose, The fractions were isolated by a step-wise increase in the ionic strength of the elution buffer. Samples A and B yielded five and six fractions, respectively. All of the fractions isolated were polydisperse containing varying pro portions of the different M(r) species associated with the whole gum. The carbohydrate composition of all fractions remained relatively cons tant with each containing similar proportions of galactose, arabinose, rhamnose and glucuronic acid. The protein content of the fractions va ried slightly (0.31-2.8%). For sample A, the protein content decreased in the order F2 > F1 > F3 > F5 > F4; for sample B the order was F1 > F6 > F3 > F2 > F4 > F5. Whereas Hyp and Ser were the principal amino a cids for the whole gums and the majority of the fractions isolated, tw o of the fractions from sample A had Asp, Ser and Glu as their princip al components. Interaction of the fractions from both samples with an artificial carbohydrate antigen (Yariv reagent) indicated that they al l contained arabinogalactan proteins (AGP). In addition, immune-dot bl ots of these fractions screened against a panel of anti-AGP monoclonal antibodies demonstrated that they all contained epitopes recognized b y one or more of these antibodies. These data describe the results of the first chemical characterization of the molecular components of gum arabic fractionated using anion-exchange chromatography. They further demonstrate the molecular complexity of this widely studied natural p roduct, and in combination with other separation procedures may provid e the key to the eventual elucidation of the biochemical synthesis of this fascinating and useful substance.