Purification and characterization of inulin fructotransferase (DFA III-forming) from Arthrobacter aurescens SK 8.001

The soil bacterium Arthrobacter aurescens SK 8.001 produces inulin fructotransferase (IFTase), and liquid chromatography–mass spectrometry (LC–MS) and carbon-13 nuclear magnetic resonance (13C NMR) analysis demonstrated that the main product of the enzyme was difructose anhydride III (DFA III). The IFTase was purified by ethanol precipitation, DEAE Sepharose Fast Flow, and Superdex 200 10/300 GL gel chromatography. Its molecular mass was estimated to be 40 kDa by SDS–PAGE and 35 kDa by gel filtration. The enzyme showed maximum activity at pH 5.5 and 60–70 °C, and retained 86.5% of its initial activity after incubation at 60 °C for 4 h. Chemical modification results suggested that a tryptophan residue is essential to enzyme activity. The N-terminal amino acid sequence was determined as AEGAKASPLNSPNVYDVT. The kinetic values, Km and Vmax, were estimated to be 0.52 mM and 0.3 μmol/ml min. Nystose was observed to be the smallest substrate for the produced IFTase. This IFTase provides a promising way to utilize inulin for the production of DFA III.