Synthesis of galactosyl glycerol from guar gum by transglycosylation of α-galactosidase from Aspergillus sp MK14

A guar gum-hydrolyzing strain, Aspergillus sp. MK14, secreted alpha-galactosidase selectively in liquid culture. Its alpha-galactosidase activity (0.820 U/ml) was much higher than its beta-mannosidase and beta-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 degrees C and the activity was stable below 50 degrees C. Enzyme activity toward melibiose was much lower than that with pNP-alpha-D-galactopyranoside. The activities toward 6(1)-alpha-D-galactosyl-mannobiose and 6(3),6(4)-alpha-D- galactosyl-mannopentaose were relatively high (86.2% and 48.4% relative to pNP-alpha-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 alpha-galactosidase could use guar gum as a good substrate (donor) in the transglycosylation. (C) 2014 Elsevier Ltd. All rights reserved.