Thermostabilization of Aspergillus oryzae β-d-galactosidase.

Abstract

The thermal stability of the Aspergillus oryzae β-d-galactosidase (β-gal) was evaluated at 60°C. The stability of β-gal was dependent on the pH, buffer, and additives. The β-gal exhibited its highest thermal stability in a 0.02 M phosphate buffer pH 6. Among all the tested additives, galactose, a competitive inhibitor of β-gal, was the upmost thermal stabilizer. A 0.15 M galactose solution caused β-gal to retain a whole of 98.65% of its initial activity after incubation at 60°C for 2 H. The second best thermal stabilizer of β-gal was raffinose. A 0.15M raffinose-β-gal mixture retained 84.41% of its initial activity after incubation at 60°C for 2H, whereas the control retained only 61.02%. The results of this study also revealed that all the tested positively charged polymers (diethylaminoethyl [DEAE] dextran and polyethyleneimine [PEI] 800, 2,000, 750,000 Da) significantly destabilized β-gal. However, these positively charged polymers exerted different effects on the β-gal's activity. PEI 750,000 significantly activated the enzyme, while DEAE dextran and PEI 800 did not exert any significant effects on the β-gal's activity. Nevertheless, PEI 2,000 significantly activated the enzyme.