Activation by polyamines, polycations, and ruthenium red of the Ca2+‐dependent glucan synthase from soybean cells

The 1,3‐β‐D‐glucan synthase in microsomal preparations from suspension‐cultured soy bean cells requires C2+ for activity. In the absence of Ca2+ the enzyme can also be activated by poly‐L‐Lys, poly‐L‐Orn and ruthenium red. Under these conditions it is either not or only slightly inhibited by La3+ and shows increased affinity for UDP‐glucose. Spermine, when present alone at 57 μM, effects relatively little activation but cooperates with 5 μM Ca2+ to greatly enhance the affinity of the enzyme towards UDP‐glucose, suggesting that both types of activation may occur at the same enzyme.