Membrane-bound chitin synthase from A3/5 had a pH optimum of 6.5, an apparent temperature optimum of 30 °C and an apparent for UDP--acetylglucosamine (UDP-GlcNAc) of 2.5 mM. Digitonin-solubilized chitin synthase had a lower (about 25% of the original activity) and more variable activity than the membrane-bound chitin synthase from which it was prepared. The activity of solubilized chitin synthase was stabilized by incorporating Allosamidin (a chitinase inhibitor) into the reaction mixture, and an approximately 3.6-fold increase in activity was observed when the reaction mixture contained dimyristoylphosphatidylcholine. Concentrations of the organophosphorus fungicide edifenphos (Hinosan) up to 25 μM had no effect on the activity of membrane-bound chitin synthase, but between 25 and 145 μM, chitin synthase activity decreased with increase in fungicide concentration. Edifenphos caused non-competitive inhibition of chitin synthase activity with an apparent of 50 μM. Membrane-bound chitin synthase preparations from cultures of grown in 250 μM-edifenphos had a much lower activity than preparations from cultures grown in the absence of the fungicide. Pre-growth of in 250 μM (but not 80 μM) edifenphos also caused a reduction in incorporation of [H]GlcNAc into chitin (washed biomass was incubated in [H]GlcNAc-containing medium lacking fungicide).


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