Studies on plant gums. Role of calcium in polysaccharide-protein interaction in the neem (Azadirachta indica) gum.

The partial removal of tightly bound Ca2+ from dialysed neem (Azadirachta indica) gum, resulted in the release of a basic protein from a highly anionic polysaccharide-protein complex as evidenced by chromatographic studies on TEAEcellulose. Complete removal of Ca2+ caused, in addition, the release of a minor heteropolysaccharide which was found in association with the basic protein. These processes were reversed on the addition of Ca2+. The gum, in addition, contained a protein-rich component accounting for 35% protein and 7·5% total carbohydrate. This component behaved as a distinct entity during ion-exchange chromatography of the native gum solutions, or which were either partially or completely depleted of bound Ca2+.