Amylolytic enzymes produced by a color variant strain of Aureobasidium pullulans
Saha, B.C. | Silman, R.W. | Bothast, R.J.
A color variant strain of Aureobasidium pullulans (NRRL Y-12974) produced amylase and alpha-glucosidase activities when grown at 28 degrees C for 4 days in liquid culture on a wide variety of carbon sources such as starch, pullulan, glucose, maltose, cyclodextrins, sucrose, xylose, and xylan. An alpha-glucosidase was separated by Q-Sepharose adsorption from the cell-free culture broth and partially purified by hydroxylapatite and octyl-Sepharose chromatography. After ammonium sulfate treatment of the culture supernatant (obtained after Q-Sepharose adsorption), the amylase fraction was separated into three active fractions by hydroxylapatite column chromatography, which were identified as alpha-amylase, glucoamylase A, and glucoamylase B. The glucoamylase A was further purified by octyl-Sepharose column chromatography. The pH optima for the action of alpha-amylase, glucoamylase A, glucoamylase B, and alpha-glucosidase were 5.0, 4.5, 4.0-4.5, and 4.5, respectively. The alpha-amylase and glucoamylase B were fully stable at pH 3.0-6.0, glucoamylase A at pH 4.5-5.5, and alpha-glucosidase at pH 3.5-7.0 for 1 h at 50 degrees C. The optimum temperatures for the action of these enzymes were 55, 50-60, 65, and 65 degrees C, respectively. The alpha-amylase, glucoamylase A, and glucoamylase B were adsorbed onto raw corn starch and degraded it. Glucoamylase B readily cleaved pullulan. The alpha-glucosidase was not adsorbed onto raw starch and did not degrade it at all. It hydrolyzed both alpha-1,4 and alpha-1,6 linkages in oligosaccharides. All four enzymes did not require any metal ion for activity and were inhibited by cyclodextrins (alpha- and beta-, 10 mM).
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