Action of α-D-glucosidase from Aspergillus niger towards dextrin and starch

The transglucosidation reactions of alpha-D-glucosidase with dextrin and starch from Aspergillus niger were investigated. When a mixture of dextrin and [U-(13)C]maltose was incubated with alpha-D-glucosidase at 25 degrees C for 5 d, [U-(13)C]glucosyl groups were linked to dextrin with a degree of polymerization (DP) of up to 14, which was detected by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). When a mixture of starch and [U-(13)C]maltose was incubated with the alpha-D-glucosidase, no [U-(13)C]glucosyl residues were transferred to the starch. Methylation analysis revealed that the chain length of the alpha-D-glucosidase-treated starch was shortened and the proportion of alpha-(1 -> 6) linkages did not increase. These results suggested that alpha-D-glucosidase catalyzed the transglucosidation reaction to dextrin with DP up to 13, but this enzyme catalyzed only the hydrolysis of starch. (C) 2009 Elsevier Ltd. All rights reserved.