DEGRADATION OF RUTIN BY ASPERGILLUS FLAVUS. PRODUCTION, PURIFICATION, AND CHARACTERIZATION OF AN ESTERASE

Aspergillus flavus produces an inducible esterase that hydrolyzes the depside, 2-(3′,4′-dihydroxybenzoyloxy)-4,6-dihydroxybenzoic acid. The activity of this enzyme may be followed by measurement of the rate of production of protocatechnic acid, which reacts with alkaline potassium ferricyanide to give a product with an absorption maximum at 540 mμ. Synthesis of the esterase is induced when the organism is grown on rutin, robinin, hyperosid, kaempferol, rhamnetin, myricetin, quercetin, and fisetin, but not when grown on apigenin, galangin, glucose, naringenin, morin, rhamnose, robinetin, or taxifolin. The esterase has been partially purified and separated from the rutinase and quercetinase enzymes. The esterase is most active at pH 4.5. Eighty percent of the activity remained after holding the enzyme for 10 minutes at 60 °C. The enzyme readily attacked the depside linkages in tannic acid but did not hydrolyze common ester substrates such as ethyl butyrate.