EFFECTS OF CALCIUM-IONS ON BETA-GLUCAN SYNTHASE ACTIVITIES IN SUSPENSION-CULTURED CELLS OF FLAX

Divalent ions, and especially calcium, highly stimulate glucan synthase activities. In the presence of magnesium, glucan synthase GSI (EC 2.4.1.12) catalyses the formation of 1-3 and 1-4 glucosyl linkages in Golgi and low-density membranes. The addition of calcium ions reveals some glucan synthases of high affinity for UDP-glucose in plasmalemma and inhibits the activity detected in low density membranes. Moreover, the glucans synthesized in Golgi are more difficult to extract. On the other hand, glucan synthase GSII (EC 2.4.1.34) catalyses the formation of 1-3 glucosyl linkages in plasmalemma while it induces the formation of 1-4 glucosyl linkages in Golgi in presence of calcium.