Isolation And Purification Of ?-Galactosidase From Hericium Erinaceus And Its Physicochemical Properties

A novel 57-k Da acidic ?-galactosidase designated as HEG has been purified from the dry fruiting bodies of Hericium erinaceus.The isolation protocol involved ion-exchange chromatography and gel filtration on a Superdex75 column.The purification fold and specific activity were 1251 and 46 U/mg,respectively.A BLAST search of internal peptide sequences obtained by liquid chromatography-tandem mass spectrometry(LC-MS/MS)analysis suggested that the enzyme belonged to the GH27 family.The activity of the enzyme reached its maximum at a p H of 6.0 or at 60°C.The enzyme was stable within an acidic p H range of 2.2–7.0 and in a narrow temperature range of 4-50°C.The enzyme was strongly inhibited by Zn2+,Fe3+,Ag+ ions and SDS.The Lineweaver-Burk plot suggested that the mode of inhibition by galactose and melibiose were of a mixed type.N-bromosuccinimide drastically decreased the activity of HEG.Moreover,the isolated enzyme displayed remarkable resistance to acid proteases,neutral proteases and pepsin.The enzyme could also hydrolyse oligosaccharides and polysaccharides.In addition,acidic protease promoted the hydrolysis of RFOs by HEG.The Km values of the enzyme towards p NPG,raffinose and stachyose were 0.36 m M,40.07 m M and 54.71 m M,respectively.These favourable properties increase the potential of the enzyme in the food industry and animal feed applications.Due to the high price of fruiting body,we used liquid fermentation of Hericium erinaceus to synthesize ?-galactosidase.Firstly,the optimum inducer,carborn source,nitrogen source and metal ions for producing ?-galactosidase by liquid fermentation of Hericium erinaceus was selected by single factor test.The culture conditions for producing ?-galactosidase by liquid fermentation were optimized by response surface method.The optimum fermentation conditions were: soybean meal 3%,glucose 2.3%,peptone 1.9%,Mg2+ 0.3%.The activity of alpha-galactosidase in the fermentation broth was 0.475 U/m L.The activity of ?-galactosidase was increased by 50.3% compared with that before optimization.This study provided a theoretical basis for the production of ?-galactosidase by liquid fermentation of Hericium erinaceus.