Abscisic Acid as Inhibitor of α‐Amylase from Aspergillus and Bacillus subtilis

Abstract

AbstractAbscisic acid (ABA) inhibited the activity of α‐amylase from both Aspergillus and Bacillus subtilis in vitro if ABA and enzyme solutions were allowed to react with each other before adding to the starch solution. If the ABA solution was put to starch before adding the enzyme, no inhibition occurred.The inhibition increased with increasing time between mixing ABA and enzyme solutions and adding the mixture to starch. It was not the absolute amounts of enzyme and ABA which were of importance for the inhibition, but the concentrations of ABA and enzyme in the ABA + enzyme mixture. Within certain limits the inhibition was proportional to the concentration of ABA, so that it should be possible to use the inhibition in quantitative tests for inhibitors.Dialysis of a mixture of ABA and enzyme showed that ABA is bound to the enzyme. The enzyme was still inhibited after dialysis for 25 h. On the other hand, partitioning with diethylether from acid water solution could free the enzyme from all ABA. Supposedly ABA acts as an allosteric inhibitor.The results may offer the foundation for one possible way to explain why inhibitors in plants sometimes inhibit growth and sometimes do not. If inhibitor, enzyme and substrate are compartmentalized, the degree of reaction should depend upon the sequence in which the three components meet each other.