Stimulation by mammalian insulin of glycogen metabolism in a wall-less strain of neurospora crassa*

Addition of bovine insulin to cells of the wallless variant FGSC4761 of Neurospora crassa (“slime”) produced several significant effects on glycogen metabolism. 1) Intracellular levels of the glycogen precursor UDP-glucose decreased 17−18% (P < 0.01) within 30 min of insulin addition. 2) Cells grown with insulin possessed 40% more glycogen than did control cells. 3) The incorporation of ¹⁴C-labeled glucose into glycogen increased 41% after 30-min treatment with 100 nM bovine insulin (P < 0.01). 4) Insulin treatment of the cells caused activation of the enzyme glycogen synthase from a glucose-6- phosphate-dependent form to an independent form. Half-maximum activation occurred with 2 nM insulin. These are similar to insulin-induced effects in some mammalian cells. In contrast, no insulin-induced effect on glucose transport could be demonstrated in these cells.