Fermentation Production, Purification and Characterization of a Fungal α-galactosidase from Trametes versicolor and Its Synergistic Degradation of Guar Gum with Mannanase

Abstract

The optimization of fermentation medium for α-galactosidase production by Trametes versicolor was investigated by using orthogonal design in shaker flask fermentation. The optimal liquid medium for α-galactosidase production by T. versicolor was consist of 1.0% soybean cake power, 0.60% galactose, 0.15% KH₂PO₄, 0.09% MgSO₄. Then, the α-galactosidase from T. versicolor (TVG) was purified and characterized. The purified enzyme, a monomeric protein with a molecular weight of 70 kDa, was purified 332-fold by means of ion exchange chromatography and gel filtration. The optimal pH and temperature of TVG with p-nitro-phenyl α-D-galactopyranoside (pNPG) as substrate were 3.0 and 60 °C, respectively. The activity of TVG was inhibited by N-bromosuccinimide (NBS), constituting evidence for the essentiality of tryptophan residue(s) at or in the vicinity of the active centre. The α-galactosidase presented a broad substrate specificity, which included pNPG, melibiose, raffinose, and stachyose with K_m values of 0.651, 3.66, 15.1, and 4.47 mM, correspondingly. Galactose acted as a noncompetitive inhibitor with K_i and K_is of 2.88 and 0.132 mM, respectively. A synergistic acceleration in guar gum degradation was found when TVG and mannanase were combined.