Studies On β-galactosidase From The Psychrotolerant Yeast Guehomyces Pullulans 17-1 Isolated From Antarctica

β-galactosidase (β-D-galactoside-galactohydrolase, EC 3.2.1.23) hydrolyzes lactose to glucose and galactose. It has many applications in chemical, food industries, and entironment-protecting et al. In recent years, the enzymes from psychrophilic or psychrotolerant microorganisms have received increasing attention as they have many potential applications in food and chemical industries. A psychrotolerant yeast strain Guehomyces pullulans 17-1 was isolated from sea sediment in Antarctica. It was found that it could yield both extracellular and cell-boundβ-galactosidase.After optimization of the medium and cultivation conditions, it was found that the yeast strain 17-1 produced over 25.3 U/mL ofβ-galactosidase within 144 h. However, the optimal of pH and temperature for the crudeβ-galactosidase were 4.0 and 50℃, respectively. Lactose could be converted into glucose and galactose and a large amount of reducing sugar could be released from milk under catalysis of the yeast culture.The extracellularβ-galactosidase in the supernatant of the cell culture of the psychrotolerant yeast strain G pullulans 17-1 was purified to homogeneity with a 2.4-fold increase in specific activity as compared to the supernatant by ultrafiltration, concentration, gel filtration chromatography (SephadexTM G-200) and cation-exchange chromatography (CM-Sepharose Fast Flow cation-exchange). The molecular mass of the purified extracellularβ-galactosidase was estimated to be 335.0 kDa on the gel filtration chromatography (SephadexTM G-200). The optimal temperature and pH of the purifiedβ-galactosidase were 50℃and 4.0, respectively. Km and Vmax values of the purified P-galactosidase for o-nitrophenyl-β-D-galactopyranoside were 3.3 mM and 9.2μmol/min.43.5% lactose could be converted into glucose and galactose after 4 h at 50℃. The matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectroscopy identified a peptide ALEEYKK which was the conserved motif of the P-galactosidases from other yeasts. The results show that the enzyme may have potential applications in food industry.