Regioselective synthesis of mannobiose and mannotriose by reverse hydrolysis using a novel 1,6-α-d-mannosidase from Aspergillus phoenicis

A novel 1,6-α-d-mannosidase was produced by Aspergillus phoenicis grown on a commercial manno-oligosaccharide preparation in liquid culture. The enzyme hydrolysed only α-d-Manp-(1→6)-d-Manp and did not act on α-d-Manp-(1→2)-d-Manp, or α-d-Manp-(1→3)-d-Manp. The 1,6-α-d-mannosidase was used for synthesis of manno-oligosaccharides by reverse hydrolysis reaction. The highest yields, expressed as percentages (w/w) of total sugar, were ∼21% mannobiose and ∼5% mannotriose, and they were obtained with 45% (w/w) initial mannose concentration at pH 4.5 after 12 days incubation at 55 °C. The disaccharide and trisaccharide products were separated and their structures determined by methylation analysis. Only 1–6 linkages were found in both of them.