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

Divalent ions, and especially calcium, highly stimulate glucan synthas e 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 Go lgi and low-density membranes. The addition of calcium ions reveals so me glucan synthases of high affinity for UDP-glucose in plasmalemma an d inhibits the activity detected in low density membranes. Moreover, t he 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 formatio n of 1-4 glucosyl linkages in Golgi in presence of calcium.