A 1,4-β-D-glucan-synthase system fromDictyostelium discoideum

Particulate membrane preparations have been isolated from culminatingDictyostelium discoideum cells. The preparations incorporated glucose from uridine 5′-diphosphate-glucose into a glucose polymer or polymers. These have been shown to be homopolymers ofβ-linked glucose. A high percentage (78% by methylation analysis) of the linkages formed are 1,4-linkages and a lower percentage (12%) are 1,3-linkages. The glucan-synthase complex present in the particulate membrane preparation has an apparent Km of 0.28 mM and a Vmax of 1.59 nmol·min−1·(mg protein)−1. The enzyme system is dependent upon Mg2+ and cellobiose for maximal activity, but is inhibited by millimolar levels of Ca2+. Particulate membrane preparations were made from cells at various times during a synchronous developmental time course and demonstrated that the glucan-synthase activity appeared at the tight-aggregate stage of development.