Regulation of glycogen synthase in Sclerotium rolfsii

Changes in glycogen, extracellular polysaccharides, glycogen synthase (EC 2.4.1.11) and cAMP were followed during growth of submerged mycelium of Sclerotium rolfsii. While glucose was present in the medium glycogen and extracellular polysaccharides accumulated to maximum levels of 40 μg (mg dry wt)^-1 and 0.3 mg (mg dry wt)^-1 respectively; they were degraded following glucose exhaustion. Neither glycogen nor extracellular polysaccharide concentrations were affected by increasing the glucose concentration in the growth medium from 0.5 to 1.5% (w/v). Following inoculation, both glucose-6-phosphate-dependent and glucose-6-phosphate-independent glycogen synthase activities increased during exponential growth, remained constant during the stationary phase as long as glucose was present in the medium, and declined rapidly after the exhaustion of glucose. The cAMP content of submerged cultures of S. rolfsii was 5 pmol (mg protein)^-1; however, upon glucose exhaustion there was a sharp increase followed by a decrease to the initial basal level. The activity of glycogen synthase in crude extracts was increased by glucose 6-phosphate and inhibited by cAMP.