Nucleotide effects on glucan-synthesis activities of particulate enzymes from Saprolegnia

Membrane-bound β-1-3- and β-1-4-glucan synthetases of Saprolegnia are affected in vitro by the presence of nucleotides. Both enzymatic activities are inhibited by uridine nucleotides. Guanosine 5′-triphosphate and ATP reduce β-1-3-glucan synthesis but stimulate β-1-4-glucan production; they also increase Vmax without effect on the Km for uridine 5′-diphosphate glucose. The stimulation by ATP could be the result of an activation or stabilization of the enzymes and might have implications for cell-wall construction during hyphal growth.