文摘
BgalA, a full-length gene (3,009 bp) that encodes a β-galactosidase, was cloned from the meso-acidophilic fungus Bispora sp. MEY-1 and expressed in Pichia pastoris. The deduced amino acid sequence of BgalA shares highest identity (55.5%) with the β-galactosidase from Aspergillus phoenicis, which belongs to the glycoside hydrolyase family 35. Purified recombinant BgalA is acidophilic, exhibiting maximum activity at pH 1.5, which is lower than that reported for other β-galactosidases. The enzyme has high pH and thermal stability and is resistant to proteases and cations found in milk. The Km and Vmax of BgalA for 2-nitrophenyl-β-d-galactopyranoside and lactose are 5.22 mM and 120.8 μmol/(min·mg), and 0.31 mM and 137.3 μmol/(min·mg), respectively. Under simulated gastric conditions, BgalA has greater stability (100%) and hydrolysis ratio (>80%) toward milk lactose than the commercially available β-galactosidase from Aspergillus oryzae (ATCC 20423). Thus, BgalA may be a better digestive supplement for alleviating symptoms associated with lactase deficiency.