Isomaltose formed by α-glucosidases triggers amylase induction in Aspergillus nidulans
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Among various α-glucobioses examined, isomaltose was the most effective inducer for amylase synthesis in Aspergillus nidulans. Amylase induction by maltose was completely inhibited by addition of cast-anospermine or cycloheximide, while induction by isomaltose was not affected by the inhibitors, suggesting that amylase induction by maltose requires inducible α-glucosidases. Disruption of the α-glucosidase A gene (agdA), the α-glucosidase B gene (agdB), or both genes did not abolish maltose-dependent induction, although amylase production induced by maltose decreased about 2-fold in the agdA/agdB double disruptant, compared with that in the agdB disruptant at all concentrations tested. Upon induction by isomaltose, amylase synthesis was enhanced considerably in the agdB and agdA/agdB disruptants. Even at 3 nM, isomaltose induced amylase production in the double disruptant, supporting the suggestion that isomaltose is a physiological inducer for amylase. Therefore, maltose must be converted to isomaltose by α-glucosidases prior to triggering amylase synthesis, but no specific α-glucosidase is required for amylase induction by maltose. Probably any α-glucosidases having isomaltqse-forming activity, including AgdA and AgdB, may participate in amylase induction by maltose.
KeywordsAspergillus nidulans α-Glucosidase Isomaltose Amylase induction
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