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

The transglucosidation reactions of α-d-glucosidase with dextrin and starch from Aspergillus niger were investigated. When a mixture of dextrin and [U-13C]maltose was incubated with α-d-glucosidase at 25 °C for 5 d, [U-13C]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-13C]maltose was incubated with the α-d-glucosidase, no [U-13C]glucosyl residues were transferred to the starch. Methylation analysis revealed that the chain length of the α-d-glucosidase-treated starch was shortened and the proportion of α-(1 → 6) linkages did not increase. These results suggested that α-d-glucosidase catalyzed the transglucosidation reaction to dextrin with DP up to 13, but this enzyme catalyzed only the hydrolysis of starch.