Some biochemical, catalytic, thermodynamic and kinetic properties of purified fructosyltransferase from wild and improved mutant-type Aureobasidium pullulans NAC8

Abstract

A low molecular weight intracellular and extracellular fructosyltransferase was purified from the wild (Wt) and improved mutant-type (Mt) Aureobasidium pullulans and its characteristics and thermodynamic properties determined. The Wt had been previously genetically modified by chemical mutagenesis. The purified fructosyltransferases from the Wt and Mt had subunit molecular weights between 13.4 and 17.0 kDa, respectively. The pH of the purified fructosyltransferase from the Wt and Mt were within 4.0–5.5. From the KM values, the fructosyltransferase from Mt showed higher affinity for sucrose than Wt fructosyltransferase. The optimum temperature obtained for the Mt intracellular and extracellular fructosyltransferase were 80 and 70 C, respectively, while the Wt extracellular and intracellular fructosyltransferase was 60 C. Most metals enhanced fructosyltransferase activity in a concentration-dependent manner except for mercury. Triton X-100 and Tween-80 enhanced the fructosyltransferase activity. Organic solvents such as acetone, ethanol, methanol, toluene and dichloromethane enhanced the enzyme activity while dimethylformamide inhibited the enzyme. From the thermodynamic and kinetic parameters (t1=2, DH , DS , DG Þ Mt fructosyltransferase was more stable to thermal inactivation than the Wt fructosyltransferase. Hence, it can be concluded that, after strain improvement of the Wt, the purified Mt fructosyltransferase was more stable to organic solvents, surfactants, and thermal denaturation, etc. compared to the Wt. This makes Mt fructosyltransferase more useful mostly in the food industry than the Wt.