A guar gum-hydrolyzing strain, Aspergillus sp. MK14, secreted α-galactosidase selectively in liquid culture. Its α-galactosidase activity (0.820 U/ml) was much higher than its β-mannosidase and β-mannanase activities (0.027 and 0.050 U/ml, respectively). The molecular weight was estimated to be 59,000 Da by SDS-PAGE. The optimal pH was 5 and it was active from pH 2.2 to 6.2. The optimal temperature was 60 °C and the activity was stable below 50 °C. Enzyme activity toward melibiose was much lower than that with pNP-α-D-galactopyranoside. The activities toward 6(1)-α-D-galactosyl-mannobiose and 6(3),6(4)-α-D-galactosyl-mannopentaose were relatively high (86.2% and 48.4% relative to pNP-α-D-galactopyranoside, respectively). MK14 crude enzyme released only the monosaccharides, galactose and mannose (Gal/Man: 0.64) from guar gum. When glycerol was added to the reaction mixture, the transglycosylation proceeded efficiently, and the synthesis of galactosyl glycerol was 76.6 mg/g of guar gum. MK14 α-galactosidase could use guar gum as a good substrate (donor) in the transglycosylation.
Keywords: Galactosyl glycerol; Guar gum; Oligosaccharides; Transglycosylation; α-Galactosidase.
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